Question about 1990 Jeep Cherokee Limited

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Need a complete wiring diagram '90 jeep laredo 4.0 of PCM,ignition,starting,ASD and other relay, also to see if there's any anti-theft for a crank no run problem. Fuel pressure good, injector pulse signal good, and unless there's a hiding fuse able link there all good

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  • shannonmcrae May 09, 2010

    Found the problem late that evening..... Ignition control module, but wiring diagram would have been extremely helpful.



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You can get a hanes book at any autoparts store.But you may want to check the tps also.

Posted on Jun 12, 2010


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Need the wiring diagram for 2005 Chevy trailblazer underhood fuse block, starting circuit.

Do you know if it is ECM/PCM or BCM controlled ?
Circuit Description (ECM/PCM Controlled)
Moving the ignition switch to the START position sends a 12-volt signal to the engine control module (ECM)/powertrain control module (PCM) Crank Request circuit. The ECM/PCM verifies that the transmission is in the PARK or NEUTRAL position. With the transmission in Park, voltage flows through the Park/Neutral position switch and feeds the starter relay coil. The PCM then grounds the control circuit of the starter relay. When the starter relay is energized it allows battery positive voltage to the starter solenoid S terminal. On some vehicles the starter will continue to crank the engine with the key released until it starts or the crank command has timed out to prevent excessive heat build up in the starter circuitry or the ECM/PCM receives an engine run flag.
Circuit Description (BCM Controlled)
Moving the ignition to the START position signals the body control module (BCM) that engine crank has been requested. The BCM verifies that theft is not active and sends a serial data message to the powertrain control module (PCM) requesting engine start. The BCM also energizes the RUN/CRANK RELAY. When the RUN/CRANK RELAY switch side closes, and the vehicle is in Park or Neutral or with the clutch is fully depressed, if equipped, supplies voltage to the starter relay coil. The PCM verifies the transmission is in Park or Neutral and the clutch is fully depressed, if equipped. The PCM will then ground the control circuit of the starter relay, closing the switch supplying voltage to the starter solenoid. On some vehicles the starter will continue to crank the engine with the key released until it starts of the crank command has timed out to prevent excessive heat build up in the starter circuitry or the PCM receives an engine run flag.

Free wiring diagrams here Enter vehicle info. year , make , model and engine size . Under system click on engine ,then under subsystem click on starting . Click the search button ,then click the blue link .
If you look at the diagram you will see the ignition switch ,when in start it sends B+ voltage to the ECM/PCM or depending on which system or engine to the BCM . When it see's this input it will energize the starter relay located in the under hood fuse box. This happens if the control module in charge see's another input from the PNP- park neutral position sensor and if no anti-theft system problems .
Good luck !

Sep 30, 2017 | Cars & Trucks

1 Answer

The red immobilizer light is staying on,the engine cranks but wont start..

You then have a ant-theft system problem an need to have the vehicle checked for DTC'S - diagnostic trouble codes . The ASD - relay supplies power to the ignition coils an too the fuel injectors .The ASD- auto shut down relay is energized by the engine computer - PCM . With the red anti-theft light on the PCM will not turn on the ASD relay cause a no start condition . You can check fuse an relays all you want ,not going to do any good . You need to see what the ant-theft systems problem is .

Feb 29, 2016 | 2003 Chrysler PT Cruiser

1 Answer

Auto shut down fuse blows when I start the truck?

This information is straight out of the 1997 Breeze/Stratus/Cirrus Factory Service Manual (Yes I paid the $90 for it years ago)

__________________________________________________ _______________

Automatic Shutdown (ASD) sense - PCM Input

The ASD sense circuit informs the PCM when the ASD relay energizes. A 12 volt signal at this input indicated to the PCM that the ASD has been activated. This input is used only to sense that the ASD relay is energized.
When energized, the ASD relay supplies battery voltage to the fuel injectors, ignition coils, and the heating element in each oxygen sensor. If the PCM does not receive 12 volts from this input after grounding the ASD reley, it sets a Diagnostic Trouble Code (DTC).

Automatic Shutdown Relay - PCM Output

The PCM operates the Automatic Shutdown (ASD) relay and fuel pump relay through one ground path. The PCM operates them by switching the ground path for the solenoid side of the realys on and off. Both realys turn on and off at the same time.
The ASD relay connects battery voltage to the fuel injectors and ignition coil. The fuel pump relay connects battery voltage to the fuel pump.
A buss bar in the power distribution center (PDC) supplies voltage to the solenoid side and contact side of the relay. The ASD relay power circuit contains a 20 amp fuse between the buss bar in the PDC and teh relay. The fuse also protects the power circuit for the fuel pump relay and pump. The fuse is located in teh PDC.
The PCM controls the relay by switching the ground path for the solenoid side of the relay on and off. The PCM turns the ground path off when the ignition switch is in the Off position. When the ignition switch is in the On or Crank position, the PCM monitors the crankshaft position sensor and the camshaft position sensor signals to determine engine speed and ignition timing (coil dwell). If the PCM does not receive the crankshaft position sensor and camshaft position when the ignition switch is in teh Run position, it will de-energize teh ASD relay.
The ASD relay and fuel pump relay are located in the PDC near the battery. The inside top of the PCD cover has a label showing relay and fuse location.

ASD and Fuel Pump Relays

The following description of operation and tests apply only to the Automatic Shutdown (ASD) and fuel pump relays. The terminals on the bottom of each relay are numbered.

' __85 ___________'
' __87A '87 '30 ___' Sorry for the crudeness of this. This is supposed to
' __86 ___________' be the relay terminals!

- Terminal number 30 is connected to battery voltage. For both the ASD and fuel pump relays, terminal 30 is connected to battery voltage at all times.
- The PCM grounds the coil side of the relay through terminal number 85.
- Terminal number 86 supplies voltage to the coil side of the relay.
- When the PCM de-energizes the ASD and fuel pump relays, terminal number 87A connects to terminal 30. This is the Off position. In the off position, voltage is not supplied to the rest of the circuit. Terminal 87A is the center terminal on the relay.
- When the PCM energizes the ASD and fuel pump relays, terminal 87 connects to terminal 30. This is the On position. Terminal 87 supplies voltage to the rest of the curcuit.

The following procedure applies to the ASD and fuel pump relays.
(1) Remove relay from connector before testing.
(2) With the relay removed from the vehicle, use an ohmmeter to check the resistance between terminals 85 and 86. The resistance shoud be 75±5 ohms.
(3) Connect the ohmmeter between terminals 30 and 87A. The ohmmeter should show continuity between terminals 30 and 87A.
(4) Connect the ohmmeter between between terminals 87 and 30. The ohmmeter should not show continuity at this time.
(5) Connect one end of a jumper wire (16 guage or smaller) to relay terminal 85. Connect the other end of the jumper wire to the ground side of a 12 volt power source.
(6) Connect on end of another jumper wire (16 guage or smaller) to the power side of the 12 volt power source. Do not attach the other end of the jumper wire to the relay at this time.


(7) Attach the other end of the jumper wire to relay terminal 86. This activates the relay. The ohmmeter should now show continuity between relay terminals 87 and 30. The ohmmeter should not show continuity between relay terminals 87A and 30.
(8) Disconnect jumper wires.
(9) Replace the relay if it did not pass the continuity and resistance tests. If the relay passed the tests, is operates properly. Check the remainder of the ASD and fuel pump curcuits.

__________________________________________________ _______________

I know you said you replaced the relay, and this is a test procedure for the relay, but I have bought bad parts in the past. The description before the test procedure at least gives you an idea of what components are wired through and controlled by the relay. One of those may be faulty. Email me if you want or need wiring diagrams and I should be able to scan them and email them to you.

Jul 15, 2015 | 1992 Dodge Dakota

2 Answers

93 Jeep Grand Cherokee, no spark from ignition coil

so gue$$ stinks sure.... why do that.?
all it takes is a scan tool to find this.

first you need to learn ASD relay rules.
to start a jeep 1993 to NOW.
the ASD most close, cranking,does it?
and most stay closed cranking and NOT drop out in 3 seconds.
that means crank for 5 seconds and if the ASD drops. at 3.?
easy huh?
if it did DROP i can tell you the ECU will set DTC errors you failed to see because you did not scan it during those 5 seconds.

first is fuses.
lets make a list. works on all jeeps 93+
  1. battery changed. to 12.6vdc reseted.
  2. keyon, CEL lamp glows, if not fuse blown to PCM (ECU)
  3. engine cranks fast.
  4. Asd realy pulls in and holds.
  5. scan tool shows, what? BINGO. DTC errors, easy huh?
  6. ok no DTC, errors, live for 5 seconds, cranking,so lost spark? must be bad coil or wired wrong. (change it 1 wire at a time?ooops)
  7. coil dead, its not DTC caused, so if no DTC that means the PCM did not see Coil ignitor errors. to coil see? i bet its got TDC;s if not then i check the coil inputs. to be sure the PCM ignitor is firing the coil correctly with my scope, oops no scope.
  8. if no scope you get to buy a new PCM. Wild guessing bad ignitor.
  9. i use a Innova 3140 scan too that does 93-95 jeeps, for about $150 only about 1.5 hrs shop labor value. and is Investment grade tool, it would have saved you 3 parts, guessed already.

Mar 18, 2015 | 1993 Jeep Grand Cherokee

2 Answers

1995jeep wrangler 2.5 cranks well but doesn,t start

If its cranking fine you have one of two problems either your not getting any fuel or you have no spark. When toy turn the key to the on positron but don't crank the car lean back and listen for a whirling sound that is your fuel pump. If you don't hear anything is probably not working spray some starter fluid in your trottle body if starts you now know your problem. If the pump is working you need to check for spark one way to check is pull a spark plug wire off the plug plug it into a spark tester and crank it if you don't see any spark the problem may be your ignition module. Hope this helps you

Mar 06, 2015 | 1995 Jeep Wrangler

1 Answer

Crank sensor for 1994 jeep laredo

why not let the PCM tell you what sensor is bad.
and do the spark test, x 4 x 6? ???
if spark is all bad.
insert the diagnostic jumper wire.
then key on,
then crank for 5 seconds.
release key
flash code will tell you if any of 3 inputs are bad, 2 sensors or spark.
The ECU cuts all fuel if it even THINKS spark is bad.
why not test spark?/ like we do for 100 years now.
its no secret how.. like 125 million google hits. (what a million hits for every year./ LOL)

this trick works on all cars and jeeps from 1988 to now.
all. all with EFI and jeep used EFI in 1988, I had one,(renix sys)

your next learning path is the ASD relay,
its just a relay that kills injection, and friends.
it drops out of the ECU thinks there is no park for 2 seconds cranking.

Feb 14, 2014 | 1994 Jeep Grand Cherokee

1 Answer

Asd relay has no power to the pcm and fuse panel inside has only half power run jumper wire to dead fuses and dash lights up and pcm powers up and jeep will start and run till jumper wire is removed

Hi, pull out the ASD relay and use a 12 volt test light to interrogate the relay socket. Hook your test light clip to ground and probe the terminals of the relay socket. There should be one hot terminal when the key is off and 2 hot terminals when the key is on. One of these is the power from fuse 6 and the other is from the ignition switch. If these are good, suspect the PCM is not turning on the ASD relay or the relay is bad. You can check for the ground signal from the PCM by moving your test light clip to battery positive and probing the other terminals in the relay socket. Again, one terminal should light the light when the key is off and both should light the light with the key on. If not, the PCM is not turning on the relay, and you should suspect your anti-theft system. Please let me know if you have questions, and thanks for using FixYa.


Jun 05, 2011 | 2001 Jeep Grand Cherokee

1 Answer

Need wiring diagram 2001 dodge caravan need power to coil

Hi, the ASD relay powers the coil. It is turned on by the PCM. Reasons the PCM might turn it off are anti-theft system (when starting) or possibly low oil pressure/high temp (when running). Please let me know if you have questions and thanks for using FixYa.




Mar 01, 2011 | Dodge Caravan Cars & Trucks

1 Answer

2000 Jeep Grand cherokee Laredo wont start. Engine turn over . No noise from fuel pump with ignition on. Replaced fuel pump and filter.Turn ignition on- pump did not run.Jumped the fuel pump at the pump...

sounds alot the the pcm it controls the fuel pump and ign system but the anti theft would keep it from starting because the key has a transponder in it programmed for that vehicle and that would kill all ign if triggered

Sep 22, 2009 | 2000 Jeep Grand Cherokee

1 Answer

Describe your 2007 Jeep Wrangle2007 Wrangler

USA car
what engine???????????
2.8L VM Motori RA 428 Diesel I4
Complete engine specs[show] 3.6L Pentastar V6
Complete engine specs[24][show] 3.8 L EGH V6
times the starter will continue to run until key is turned off.
that is starter relay bad or the puter running it gone nuts.
or bad starter
next time when starter latches up, pull the relay
if it kills the cranking its bad relay or puter
if not, bad starter. all in 1min work..
and a very very serious first ORDER fix first problem
runs on test fuel. but you failed to keep it running for the 2 -3 second JEEP RULE.
if you had here is the results. (logic) hard.
1: i can keep it running with spray need a video?
yes, means ASD is not dropping out
2: no? ASD is killing the engine on purpose. and scan tool told you.

cranks no start
you said,
"No codes." if really true , there is no fuel pressure.!
if not true, its done wrong. so scan correctly THIS time.
is the skim light glowing in the dash cluster, if yes, it will not start
by DESIGN. SKIM is the immobilizer and DOES!

you must scan WHILE l its failing, not after, WHILE.
HOW TO SCAN correctly on JEEPS, (no starts)
key on, see scanner working? now, it must, if not ask.
crank or 5 seconds, (1 potato , 2 potata, 3,4,5.
release key, ( 4 and 5 are overkill but why not?)
do not turn key off or say 2 minutes, get PCM time to REPORT.

scan (2008 or newer scan tools work, CAN-BUS certified)
the tool then tells you why the ASD RELAY dropped killing starting (by DESIGN)
try to know SKIM is and option, so.... me blind can see car

runs on test fuel longer that 3 seconds, by hand, means.
all is working mostly, the fuel pressure gauge needs a jeep hose kit to work so/....... the pump needs power to work,

now the acid tests
i have 2. acid tests lacking a real scan too;..
spark timing light connected up.
you crank and spark dies, AFTER 2-3 seconds into crank/start
cycle means ASD dropped.
connect meter to injector 12vdc power feed its a daisy chain
12vdc dies, at 3seconds of crank, or dies
at 3 seconds of running,
if true PCM did that , and is ASD drop doing that
running any jeep for 1 second on test fuel is a waste of time
it tells too little
learn that jeeps can drop a ASD at 100mph
any time it wants. and only scanning while it drops
tells you why, unless the SKIM lamp glows,

Mar 03, 2017 | Jeep Wrangler Cars & Trucks

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