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PCM not working on 2000 Jeep Cherokee 4.0 engine.

I hooked up a manual switch for the electric fan for cooling engine . With a fuse. Could this have shorted out my pcm Main cmputer on my 2000 Jeep Cherokee . 4.0 engine

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  • Richard Scordino May 11, 2010

    If you tapped into the fan power wire without unplugging it from the harness, it's possible to damage system, but I would think at best it would damage the relay. (the way they wire these things though nothing would surprise me) Is your jeep not starting now? Have you done or tried to do a code check? What were the results?



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Posted on Jan 02, 2017

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SOURCE: 2001 jeep grand cherokee no start, no cam signal or ASD control from pcm


Posted on May 15, 2009

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SOURCE: where is the pcm on 1997 jeep grand cherokee 6 cyl?

I don't think the PCM is your problem, is the check engine light on? It could be you idle air control motor this is located on the throttle body, but because this happens while driving I am thinking you will need to replace your crank shaft position sensor it is located on the transmissinon bell housing it is very hard to replace without the correct tools. If the check engine light is on take it to a local auto parts store and ask if they can check the check engine codes for you they usally will do this for free.

Posted on Jun 03, 2009

  • 6982 Answers

SOURCE: jeep grand cherokee stalls after warming up

You need to check components again when the engine is hot and in no-start condition, otherwise, you will get bad info...obviously whichever part is doing this works fine cold. ones that react most to heat are crank pickup, ignition coil and the fuel pump.(bad ones get hot and bind up)

Posted on Jun 07, 2009

  • 244 Answers

SOURCE: how do i reset my pcm on my jeep grand cherokee?

try disconnecting the NEGATIVE cable on the battery for 10-20 minutes. re-connect it. start the vehicle and drive it for a few miles to let the pcm reset. (make sure the key is off and out, just to make sure you don't fry something when you remove the negative-black wire cable!!). don't short it against the positive-red!
make sure the negative connector (on the cable) is isolated from the frame, or it will still be grounded! wrap some plastic around it, or something!
good luck!

Posted on Sep 22, 2009

  • 2984 Answers

SOURCE: where is the pcm located on a 1997 jeep cherokee

Removal & Installation

  1. Disconnect the negative battery cable.
  2. Remove the coolant reserve tank and disengage the three electrical connectors from the PCM.
  3. Remove the three PCM mounting bolts and carefully remove the PCM.
  4. Installation is the reverse of removal.

Posted on Apr 18, 2010

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2009 chevy hhr speakers don't work and a/c radiator fan won't come on

What engine does it have ?

Cooling Fan Control 2.0L
The engine cooling fan is a variable speed fan. The engine control module (ECM) controls the fan speed by sending a pulse width modulated (PWM) signal to the cooling fan control module. The cooling fan control module varies the voltage drop across the engine cooling fan motor in relation to the PWM signal. The cooling fan speed can be adjusted from 10 percent to 94 percent duty cycle. 94 percent is considered high speed fan.
Cooling Fan Control 2.2L or 2.4L
The engine cooling fan system consists of one cooling fan and one relay. Voltage is supplied to the relay through a fuse. The engine control module (ECM) controls the fan operation by grounding the cool fan relay control circuit. When the cool fan relay is energized, voltage is delivered to the cooling fan motor. The cooling fan motor is grounded through its own ground circuit.
When the request for fan activation is withdrawn, the fan may not turn OFF until the ignition switch is moved to the OFF position or the vehicle speed exceeds approximately 10 mph. This is to prevent the fan from cycling ON and OFF excessively at idle.

Just one speaker doesn't work ? Do you know how to do automotive electrical testing ? That's how to find both your problems . Speakes work by electrical inpluse's . The A/C radiator ( condenser ) fan also works by B+ voltage through a fuse an a relay , controlled by the engine electronic control module or PCM - powertrain control module . When you push the A/C turn on button , it sends a signal to the PCM . The PCM will then energize the radiator fan relay turning on the fan . Check fuse in the under hood fuse box , If the fuse is blown you have a electrical short , too much current flow . Plus if the PCM sees too much pressure in the A/C system it will not let the A/C work .

Mar 31, 2017 | Cars & Trucks

1 Answer

Need a wiring diagram of the 2 wires from the temp sending unit that controls the temp gauge and cooling fans on a 99 grand am gt. Need to see where they go They disappear behind the engine

The PCM regulates voltage to the coolant fan relays, which operate the fans. Refer to Engine Controls.

Engine Cooling Fan Description - Electric
The electric cooling fans are used to lower the temperature of the engine coolant flowing through the radiator. They are also used to cool the refrigerant (R-134a) flowing through the A/C condenser.
The electric cooling fan operates when the engine cooling temperature exceeds a certain value. The cooling fan on this engine is controlled by the PCM. The cooling fan has one speed. The PCM turns the cooling fan ON by grounding the coil of the cooling fan relay when certain conditions are met. When the A/C is requested, the cooling fan will also be turned ON.
Power for the cooling fan motors are supplied through Cool Fan #1 and Cool Fan #2 relays. The cooling fan relays are energized when current flows from the fuses in the Cell 23: Cooling Fan Controls , and through the relay coils to ground through the PCM. The Low Speed fans control circuit is grounded for low speed fans operation. During low speed fans operation, both fans run at a slow speed. The High Speed fans control circuit is grounded for high speed operation. During high speed fans operation, both fans run at high speed.
Important: When certain Diagnostic Trouble Codes (DTCs) are present, the PCM may command the cooling fans to run all the time. It is important to perform Powertrain On Board Diagnostic (OBD) System Check prior to diagnosing the engine cooling fans.
If a problem that involves the low speed cooling fan relay control circuit exists, DTC P0480 should set. If the problem affects the high speed cooling fan relay control circuit, DTC P0481 should set. A problem with the ECT sensor should set DTC P0117, P0118, P1114, or P1115. Any of these DTCs will affect cooling fan operation and should be diagnosed before using the Cooling Fan Diagnosis tables. The Cooling Fan Diagnosis tables should be used to diagnose the PCM controlled cooling fans only, if a DTC has not set.

The engine coolant temperature (ECT) sensor (3) is a thermistor, a resistor which changes value based on temperature, mounted in the engine coolant stream. Low coolant temperature produces a high resistance (100,000 ohms at -40°C) (-40°F), while high temperature causes low resistance (70 ohms at 130°C) (266°F).
The PCM supplies a 5 volt signal to the ECT sensor through a resistor in the PCM and monitors the terminal voltage. Since this forms a series circuit to ground through the ECT sensor, high sensor resistance (low temperature) will result in high PCM terminal voltage. When the resistance of the ECT sensor is low (high temperature), the terminal voltage will be drawn lower. This terminal voltage indicates engine coolant temperature to the PCM.
A hard fault in the ECT sensor circuit should set either a DTC P0117 or P0118. Remember, these DTCs indicate a malfunction in the engine coolant temperature circuit, so proper use of the DTC table may lead to either repairing a wiring problem or replacing the sensor, to properly repair a problem.

The engine coolant sensor is an input to the PCM , Two wire's both go to the PCM .An the PCM turns on the cooling fans !

DTC P0480 Cooling Fan Relay 1 Control Circuit
DTC P0481Cooling Fan Relay 2 Control Circuit
The Body Control Module (BCM) request the cooling fans. The BCM sends a Class 2 message to the PCM in order to enable the fans based on various inputs. Thebattery voltage travels to all three cooling fan relay coils. The PCM enables cooling fan relay #1 by providing the ground path. The PCM enables cooling fan relays #2 and mode control together by providing a ground path. The left and right cooling fans are connected in series. This will enable both fans on low speed when the fan #1 relay is energized. When all three fan relays are energized, both fans will operate at high speed. The high speed is possible because the fan relays are wired in a parallel circuit. When the PCM detects that certain DTCs are set, the PCM will enable the cooling fans.
The PCM will enable the engine cooling fans when certain Diagnostic Trouble Codes are set.

Important: A short to ground will cause an open fuse(s). Before performing this diagnostic procedure, inspect the fuse(s) for an open.
Did you perform the Instrument Cluster System Check?
Go to Step 2
Go to Instrument Cluster System Check
Turn the ignition switch to the ON position.
With the scan tool select Instrument Panel Cluster, Special Functions, Instrument Panel Cluster (IPC) gauges.
Perform the Coolant Gauge Sweep Test.
Does the coolant temperature gauge complete a full sweep when commanded?
Go to Powertrain On Board Diagnostic (OBD) System Check in Engine Controls
Go to Step 3
Replace the instrument cluster. Refer to Instrument Cluster Replacement .
Did you complete the repair?
Go to Instrument Cluster System Check

Your best bet would be to take your vehicle to a qualified repair shop that knows how the system works . An has the tools to diagnose the problem .

Nov 13, 2016 | 1999 Pontiac Grand Am GT

2 Answers

RADIATOR ENGINE COOLING Electric fan override 1996 Jeep Cherokee Sport

RAD FAN IT IS. Engine cooling fan.
redux 1, 1996 XJ, 4.0L engine.
Rad fan, only.
RAD fan on,with PCM wanting it OFF. bypass.

or want fan to run fording streams. NO.
ask your offroad buddies what fording streams means. (hint it's not FORD car)
We do this offroad so the fan blades dont crash and break off, as they hit deep water.
posted vast times the free schematic, off the FSM book. links.
then chapter 8w (wiring)
then fan in index.
then , easy no?
pdf page 19 is the real index.
PAGE exact. XJ.
8w 42-9 is relay,pdf page 223
so lets go there.
WIRE COLOR ANSWERED !! below. 1st page of 8w show what color codes mean on all jeeps made.
the DB-PK wire on the relay D13
if grounded by any switch turns on the relay and fan.
do not use 12v power there or say goodbye to PCM. boom. (it will blow it up)
even grounding it can... (avoid the $500+ mistakes)

the free FSM

pg 223 pdf page, chapter 8w,
Relay FAN. ECU runs it there are no thermal switches, the ECT readings do all this. and very well.
the coil has 12vdc power keyon, the other rlay pin is hot all time.bat pin
top right.

see my switch ?if you use center off version switch
mark center FORD
eg: normal(pcm), ford, BYpass (or active)
or normal, dead, force on.


the first image is the risky way... but some do that. just SPST switch. (2 pins toggle, id use the 3pin way)

May 29, 2016 | 1996 Jeep Cherokee Sport

2 Answers

What does this mean?????????????

P0480 Cooling Fan Relay 1 Control Circuit OBD-II Trouble Code Technical Description Article by
Don Bowman
ASE Certified Automotive Tech

Cooling Fan Relay 1 Control Circuit
What does that mean? This is a generic powertrain diagnostic trouble code (DTC), which means it covers all makes/models, 1996-newer. However, specific troubleshooting steps will vary depending on the vehicle.
If your vehicle's check engine light comes on and after pulling the code you find a P0480 displayed, if refers to the engine cooling fan circuit. It is a generic code applying to all OBD II (on board diagnostics) vehicles.
While you are driving, air in sufficient quantity is passing through the radiator effectively cooling the engine. When you bring the car to a stop no air is passing through the radiator and the engine begins to increase in temperature.
The PCM (powertrain control module) senses the increase in engine temperature through the CTS (coolant temperature sensor) located near the thermostat. When the temperature reaches about 223-degrees F (value depends on make/model/engine), the PCM will command the cooling fan relay to turn on the fan. It does so by supplying the ground to the relay.
There is a problem within this circuit causing the fan to fail to operate allowing the engine to overheat while sitting still or driving at a slow speed. When the PCM attempts to activate the fan and senses the command and the result do not match, the code is set.
NOTE: P0480 speaks of the basic circuit, however codes P0481, and P0482 relate to the same problem with the only difference is they relate to the different fan speed relays.
Symptoms Symptoms may include:

  • Check engine light (malfunction indicator lamp) illumination and code P0480 set
  • Engine temperature will rise when the vehicle stops and idles
Potential Causes The causes for this DTC may include:
  • Faulty fan control relay 1
  • Fan control relay harness is open or shorted
  • Circuit electrical connections poor
  • Faulty cooling fan 1
  • Faulty coolant temperature sensor
  • Fan cooling fan harness is open or shorted
  • Cooling fan circuit poor electrical connection
  • Intake air temperature (IAT) failure
  • A/C selector switch
  • A/C refrigerant pressure sensor
  • Vehicle speed sensor (VSS)
Diagnostic and Repair Procedures It is always a wise idea to look up the technical service bulletins (TSB) on your particular vehicle to see what type complaints have been coming in to the dealer service department related to this code. Search using your favorite search engine "technical service bulletins for ....." Look up the code and the type of manufacturer recommended repair. This is also a good idea before buying a vehicle.
Many vehicles will have two engine fans, one for engine cooling and the second for cooling the air conditioning condenser, and additional cooling for the engine.
The fan that is not in front of the air conditioning condenser is the main cooling fan and the one to concentrate on initially. Additionally, many vehicles have multi-speed fans requiring as many as three fan speed relays for low, medium and high.
Open the hood and do a visual inspection. Look at the fan and make sure there is no obstruction in front of the radiator blocking airflow. Spin the fan with your finger (make sure the vehicle and key is off). If it will not spin the fan bearings are shot and the fan is bad.
Check the electrical connection at the fan. Pull the connector apart and look for corrosion or bent pins. Repair if necessary and use dielectric grease on the terminals.
Open the fuse block and inspect the cooling fan relay fuses. If they are good pull the cooling fan relays out. The bottom of the fuse block lid will usually indicate placement, but if not, look in the owner's manual.
The vehicle's PCM's function is to act as a ground to operate components, not to supply power. The fan relays are nothing but a remote light switch. The fan as well as other apparatus draws too much amperage to be safe in the cockpit, so it's kept under the hood.
A constant power supply from the battery is present on a terminal in each of the relays. This one turns on the fan when the circuit is closed. A switched terminal will be hot only when the key is on. The negative terminal in this circuit is the one used when the PCM wishes to active the relay by grounding it.
Look at the circuit diagram displayed on the side of the relay. Look for the simple open and shut circuit. Verify the battery positive terminal in the relay block with constant power. The opposite side goes to the fan. Use a test light to find the hot terminal.
Jump the battery terminal to the fan harness terminal and the fan will operate. If not, disconnect the fan connection at the fan and using an ohmmeter check the continuity between the fan side of the relay terminal and the connector at the fan, If there is continuity the fan is bad. If not the harness between the fuse block and the fan is faulty.
If the fan operated, check the relays. Look at the side of the relay for the switched power terminal or just turn the key on. Check the terminals for an additional power terminal and look where it would be on the relay.
Jump the battery plus terminal in the first test with this switched terminal and place an additional jumper from the negative terminal on the relay to ground. The switch will click on. Use an ohmmeter to test that the constant battery terminal and the fan harness terminal have continuity meaning the circuit has closed.
If the circuit has not closed or the relay has not clicked, the relay is bad. Check all the relays in the same fashion to be sure they are all working.
If there was no switched power at the relay, the ignition switch is suspect.
If they prove to be good, check the CTS with an ohmmeter. Pull the connector off. Let the engine cool and put the ohmmeter on the 200,000 scale. Probe the sensor terminals.
The reading will be about 2.5. For precise readings consult a service manual. Accuracy isn't necessary since all sensors may be different. You just want to know if it's working. Reconnect it and warm the engine.
Shut the engine down and pull the CTS plug again. Check it with the ohmmeter, there should be a big change in resistance, if not the sensor is bad.
If the above procedure could not find a failure, the probability is that a poor connection to the PCM or the PCM itself is at fault. Do not go any farther without consulting your service manual. Disconnecting the PCM could cause loss of programming and the vehicle may not start unless towed to the dealer for reprogramming.

Sep 23, 2015 | 2006 Volkswagen Jetta

3 Answers

2007 jeep commander cooling fan not working, what's problem, is there a fuse ?

What engine does yours have , 3.7 ,4.7 , 5.7 l There are different cooling fan's , electric , Electronic hydraulic ! There are fuse's , relays , electronic control module .

May 05, 2015 | Jeep Cars & Trucks

1 Answer

My ac is not working I have a Chevy Tahoe 2005 the fans won't turn on either .

Hi Maria , The A/C system wouldn't keep the fans from running but none working cooling fans will keep the A/C from working ! This is a fairly complex system if your not familiar with this sort of thing ! I will add the description from the factory service manual.
Cooling Fan Control - Two Fan System
The engine cooling fan system consists of 2 electrical cooling fans and 3 fan relays. The relays are arranged in a series/parallel configuration that allows the powertrain control module (PCM) to operate both fans together at low or high speeds. The cooling fans and fan relays receive battery positive voltage from the underhood fuse block.
During low speed operation, the PCM supplies the ground path for the low speed fan relay through the low speed cooling fan relay control circuit. This energizes the low speed fan relay coil, closes the relay contacts, and supplies battery positive voltage from the low fan fuse through the cooling fan motor supply voltage circuit to the left cooling fan. The ground path for the left cooling fan is through the cooling fan s/p relay and the right cooling fan. The result is a series circuit with both fans running at low speed.
During high speed operation the PCM supplies the ground path for the low speed fan relay through the low speed cooling fan relay control circuit. After a 3 second delay, the PCM supplies a ground path for the high speed fan relay and the cooling fan s/p relay through the high speed cooling fan relay control circuit. This energizes the cooling fan s/p relay coil, closes the relay contacts, and provides a ground path for the left cooling fan. At the same time the high speed fan relay coil is energized closing the relay contacts and provides battery positive voltage from the high fan fuse on the cooling fan motor supply voltage circuit to the right cooling fan. During high speed fan operation, both engine cooling fans have there own ground path. The result is a parallel circuit with both fans running at high speed.
Do you have a check engine light lit ? The thing to do would have it check at the dealer or a ASE certified repair facility ! They could hook up a advanced scan tool an diagnose fairly quick ! Or you could find a wiring diagram an try testing with a volt meter yourself ! But watch yourself so you don't short out the PCM - engine computer !

May 01, 2015 | AC Cars & Trucks

1 Answer

Over heating cant find cooling fan relay

Gas or Diesel?
check fuses first! then scan it, the PCM will set DTC errors
if power feeds to the fan are dead, not scanning cars first is a travesty to (labor, time, parts wasted etc) even $10 scan tool works on our USA cars this year.

first off there are 2 systems.
and you never said what engine.
no engine, we must guess.
why work on any car, not knowing whats under the hood.
cylinder count 6,
displacement. 4.0 (wild guessing )
at the least. the big engine has the Hydr. system only.
wj jeep

4.0L or 4.7L engine.
ill answer for 4L , 5million sold.
TEST 1 (fan) parked and ran and purposefully overheated
this is a SOP FSM test , to see if the fan trips at the correct temperature !
if the fan does not work, parked, and overheating there are only these things wrong. ( any volt meter finds this easy)
1: ECT not showing overheat, to PCM ( use a scan tool !!!)
2: PCM cant see ECT , wires bad to ECT. sensor.
3: PCM fails to close relay (volt meter checked) due to above.
4: relay bad, or missing or wires to it bad. coil must be 12vdc hot.
5: relay output at 12vdc but fan dead, that is a dead fan, (hot)

in all cases bad wires and fuses and connections bad.
the 4.0L engine fan is a hybrid, has electric fan and thermal fan on front of water pump. so there are 2 tests.


its all there.
cav 13/14 PDC socket is it.

open hood, open lid, see lid words, its there. fan.


Mar 18, 2015 | 2002 Jeep Grand Cherokee Limited

1 Answer

Cooling fan does not run?

At the main fuse and relay box, check the 30A EGI INJ fuse. If OK, the main relay closes to apply power to the cooling fan relay. Next, check the 30A FAN 1 and FAN 2 fuses.If OK, power is being applied to the fan control module. The PCM processes engine coolant temperature sensor input and sends a signal to the fan control module which, in turn, causes the cooling fan motor to operate. Fan failure could be caused by malfunction of the cooling fan relay, the fan control module, the engine coolant temperature sensor, the cooling fan motor itself, or the PCM

Oct 06, 2012 | 2005 Mazda MPV

2 Answers

I have a 1999 Alero 3.4 V6 the cooling fans won't run. I checked the fans they both work if I unplug the harness for the temp sensor,the relays and fuses are fine,I replaced the coolant temp sensor and...


Sep 06, 2011 | 1999 Oldsmobile Alero

1 Answer

Engine Cooling problem 2000 Jeep Cherokee 4 cyl

Although the 4 cylinder is too underpowered to have air conditioning in my opinion, it still shouldn't overheat within 10 minutes unless something is wrong. If your Jeep doesn' not overheat when you are driving WITHOUT AC on then your compressor might have a problem and causing the engine to work too hard to turn it.

But if it overheats without the AC on, then the first thing you need to do is check the cooling fan and see if it operates! There has been a lot of problems with the cooling fan relay on this model. If that isn't it, then move to changing the thermostat and checking the water pump.

Jul 03, 2011 | 2000 Jeep Cherokee

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