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How can I test the PCM to know whether it needs replacing or not

The alternator was over charging (17.5 volts) and cooked the battery (boiled it over). I replaced both with new and now the engine is hard to start and after it does start it idles fine for 4 or 5 minutes and then goes to fast idle and it won't release back to normal idle. I have not had the chance to check the sensors for their voltages and resistance but was told that when the alternator started over charging that it probably burnt up the computer (PCM)

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  • mikelikes24 Jan 23, 2013

    I have installed both a new alternator and new battery. I understand the amps and voltage checks and have preformed both tests. That part checks out. I'm concerned that now that they have been replaced with new, that the computer was fried also. especially now that it goes to fast idle after 4 minutes or so and won't release back to the normal idle state.

  • mikelikes24 Jan 23, 2013

    The truck ran fine until the alternator went bad and had no idle issues at all. I'm not wanting to troubleshoot this by replacing parts until I get it right. I want to prove what the issue is first and then replace it with a new piece.

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  • Cars & Trucks Master
  • 21,873 Answers

Given the age of the truck, and the lack of diagnostic abilities of the computer Ford used in that year, I would get a used computer to eliminate it from the list of possible problems.
The computer could be "tested" but not without taking it apart to look for problems in the circuit board and components.
And yes it is very possible the bad alternator fried some diodes and drivers on the circuit board.

Posted on Jan 23, 2013

  • mikelikes24 Jan 23, 2013

    the one thing that confuses me is the truck will start and seem to run fine for a few but then goes to the fast idle and when I shut it off it will crank but not start back up. I read the codes and it seemed like every code in the book was there. After reading all the codes it just doesn't make any sense. Thanks

  •  Stephen
    Stephen Jan 23, 2013

    Did you clear the codes, and did they all come back again ? What do you have to do to get it to start again ?

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fastboyz
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SOURCE: 1999 Ford Escort idle problems

you need to look for a vacume leak thsi would also make your IAC valve go beyond range.good luck

Posted on Sep 12, 2008

localwonder
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SOURCE: 1998 Monte Carlo alternater not charging

Ok, i understand that you have replaced the alternator, but there seems to be a non charge state in this case. i recommend checking the charging system. use the procedure below to isolate this issue.

Wear protective eye wear and clothing and remove all jewelry when checking your battery and charging system. Jewelry is a good conductor of electricity and is not recommended. Most batteries wear out every 3 to 5 years and need to be replaced. Always replace your battery with an equal replacement battery to assure proper operation. Automotive batteries have a +positive terminal (red), - negative terminal (black). The battery in this illustration has a protective cover over the positive terminal to prevent short circuit in case of an accident. Electricity is stored in the battery and then supplied to the vehicle when the engine is not running. While the engine is running the vehicles alternator charges the battery for future use. (Note: never disconnect the battery while the engine is running. If the battery cable is disconnected from the battery a spark can be generated which can cause the battery to explode or a major electrical malfunction to occur.)

To check a battery surface voltage, remove the positive terminal protective cover. Connect the +positive side meter lead (red) to the positive side battery terminal. Connect the - negative (black) side meter lead to the negative battery terminal. With the vehicle not running and the car sitting over night the battery voltage should be between 12.5 and 12.8 volts.(You will need to use a voltmeter for this testing procedure)

The alternator is rotated by a drive belt driven by the vehicles engine while it is running. Electrical voltage and amperage are generated to recharge the battery and supply voltage to the electrical system of the car. The alternator is held in place with mounting bolts. There is a main electrical wire on the rear of the alternator that supplies voltage to a main voltage junction box. If your alternator is not charging properly, your battery will slowly drain down from operating all the electrical systems in your car and stop the car from running.(most non charge states will be the cause of a loose belt or a low tension rate, due to a mis-adjusted alternator. make sure you have enough tension in the belt for full rotation of the alt pulley)

Next, you will need to check the alternators output with the Amp meter.

Testing the amperage output of the alternator is good for measuring the amount (not the level) of voltage the alternator can produce. This test can be tricky because if the alternator is weak it can still show it as producing amperage. Which is good, but if the voltage is low, it will still allow the battery to go dead. To check the amperage output of an alternator an amp meter is needed. Once the meter is connected start the engine. Next turn on all electrical accessories and raise the engine idle to about 1200 RPM. The alternator should output the max amperage it was designed to produce. Example: a 90 amp alternator should output about 88 amps. Note: An alternator cannot sustain maximum output for long periods of time. If the alternator is forced to operate at maximum output it will overheat and fail. An alternator is designed to operate at max amperage output only for a reasonable amount of time.

((Connect the voltage meter lead the same way you would in a battery static voltage check, Start engine (do not drive) at engine idle the voltage should be between 13.6 to 14.3 volts. If not the alternator may need replacing.)))

Posted on Sep 07, 2009

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SOURCE: 1994 Nissan Altima GXE Engine miss

check your EGR and for vacuum leaks

Posted on Oct 03, 2009

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SOURCE: 2002 impala 3.8L 180,000kms. Having

it is possibly the throttle position sensor(tps) malfunctioning. basically the computer or "brain" of the car thinks the throttle is in a different position than it really is and automatically makes adjustments to fuel, air ect.... based on these false readings from the sensor thus causing the engine to react a little different when you expect to have power.

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SOURCE: replaced egr valve pressure sensor upstream and

where is da egr control solen noid located on the 1996 ford explorer?

Posted on Mar 09, 2012

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P2500 starts but won't stay running


P2500 Generator Lamp/L-Terminal Circ Low

Indicator

This code indicates that a fault has been detected in the generator lamp control circuit. The PCM may have also detected an abnormal voltage reading from the vehicle battery, starting, or charging system.

Code Set Parameters

In the event of generator lamp control circuit fault, a trouble code will be stored and a service engine soon lamp will be illuminated. Some models require multiple drive cycles (as many as 8) with a failure in order for the service engine soon lamp to be illuminated and others will activate it on the initial failure.

Symptoms

This code indicates that a fault has been detected in the charging system circuit. The PCM may have also detected an abnormal voltage reading from the vehicle battery, starting, or charging system.

Common Causes

The most common cause of this code can be traced to a faulty alternator. Other causes could include a bad battery or starter, open or shorted wiring or battery cables, insufficient battery primary or secondary grounds, defective voltage regulator, corroded battery terminal ends, a faulty PCM (rare), a large battery drain, or a defective battery.

Common Misdiagnosis

Technicians report that batteries and starters are often replaced in error when the alternator is either not charging or overcharging. If the battery is discharged, charge it and test the vehicle charging system to make sure that it is operating properly.

Diagnosis

  • The starting/charging system is monitored by the PCM whenever the key is placed in the "ON" position, as is the generator lamp circuit for the instrument panel
  • When the engine is running, the PCM is programmed to anticipate between 13.8 and 14.4 volts from the charging system
  • If a voltage reading that either exceeds or underachieves, a code will be stored and a service engine soon lamp illuminated
  • Some vehicle models (especially Chrysler) also use the PCM to regulate charging system voltage
  • System voltage malfunctions related to the PCM are much more common in vehicles equipped with this type of system than in other systems. Before beginning your diagnosis, make sure that the battery is fully charged
  • If the battery fails to take or hold a charge, it should be replaced. Several tools will be instrumental in successfully diagnosing this code
  • A suitable OBD-II scanner (or code reader) and a digital volt/ohmmeter will be most helpful in performing a successful diagnosis
  • Begin with a visual inspection of all wiring and connectors
  • Repair or replace damaged, disconnected, shorted, or corroded wiring, connectors, and components as necessary
  • Always retest the system after repairs are completed to ensure success. If all system wiring, connectors, and components (Including fuses) appear to be in normal working order, connect the scanner (or code reader) to the diagnostic connector and record all stored codes and freeze frame data
  • This information can be extremely helpful in diagnosing intermittent conditions that may have contributed to this code being stored
  • Continue by clearing the code and operating the vehicle to see if it returns
  • This will help to determine whether or not the malfunction is intermittent
  • After the codes are cleared, test drive the vehicle to see if the code returns
  • If the code fails to immediately return, you may have an intermittent condition
  • Intermittent conditions can prove to be quite a challenge to diagnose and in extreme cases may have to be allowed to worsen before a correct diagnosis can be made
  • Continue with a visual inspection of the battery and battery cables
  • Should you find excessive corrosion on the battery terminals, suspect a poor battery connection
  • If this is the case, disconnect the battery cables from the battery (always disconnect the ground cable first and see manufacturer's recommendations for disconnecting/reconnecting the battery) and remove the corrosion from the battery posts and terminals
  • Reconnect the battery and retest the charging system
  • Connect the starting/charging system tester to the battery and perform a load test
  • If the battery fails the load test, replace it
  • If the battery passes the load test, leave the tester connected and start the engine
  • Observe the voltage readings on the tester and compare your findings with manufacturer's specifications
  • Replace starting/charging system components as required
  • Typical alternator output should read approximately 14 volts with the engine started and no accessories or lighting turned on
  • Leave the tester connected and use the amp probe to test the starter current draw
  • Compare your findings to manufacturer's specs and repair or replace starting system cables or other components as needed. The generator lamp circuit is used to activate a charging system indicator in the instrument panel if system voltage is abnormal
  • Voltage readings that are too low may indicate worn brushes in the alternator
  • High voltage readings may be indicative of a defective voltage regulator (usually integrated in the alternator but some are part of the PCM)
  • Before performing any continuity and resistance testing on the generator lamp circuit, be sure to disconnect the wiring from the instrument panel to prevent damage to system controllers and circuit boards
  • Consult the vehicle service manual for reference voltage readings and other precautions. If the starting/charging system are in proper working order, you will need to test secondary wiring
  • Disconnect the alternator connector and test all circuits using the digital volt/ohmmeter
  • If alternator wiring values are in line with acceptable specifications, disconnect the PCM connector and perform a continuity test on all system circuits
  • Compare actual findings with manufacturer's specifications and repair open or shorted electrical wiring as necessary. If the malfunction has still not been rectified, suspect a defective PCM.

Nov 09, 2016 | Cars & Trucks

3 Answers

2004 ford freestar 4.2l Not charging, new alternator tested and working new battery.


Hotrod, Recheck,clean and tighten all connections. If you say you had new alternator tested and is working OK, the new battery must be defective. With the van running, use a DVO meter and check the battery, if it shows above 14 volts then the alternator is OK, a good battery should show 12.4, that leaves either a faulty battery not holding a charge or you have a parasitic draw(something draining battery). Which would have to be diagnosed by a good Tech.
Check the attached links,instruction and guides, Good luck
"I hope this helped you out, if so let me know by pressing the helpful button. Check out some of my other posts if you need more tips and info."
How To Check Charging System EricTheCarGuy
How To Perform Parasitic Draw Test EricTheCarGuy
Battery or Alternator How to Tell Which one is Bad and QandA
Car won start Battery or Alternator Find out



May 25, 2016 | Ford Cars & Trucks

2 Answers

Voltage problem.


the problem is in the voltage regulator
maximum voltage is controlled at 14.5 to 14.8 volts depending on whether the voltage regulator is in the ECM or not
but 14.8 would be max allowed any higher can damage the electronics of the vehicle including the ECM
take it to an accredited auto electrician, have it test and adjusted or the regulator replaced

Nov 25, 2015 | Buick Rendezvous Cars & Trucks

1 Answer

Battery light wont stop coming on but alternator is good and battery is good and starter just replaced and all cables and fuses are good and car wont run unless you hold he gas pedal down it is a 2005...


engine running what is the battery voltage.if around 11 volts and 12 volts it is not charging. around 13.5 volts it is charging.alternator give to pcm the volt charge then the pcm send a ground to cluster to turn off charging light

Sep 14, 2013 | 2004 Pontiac Grand Am

1 Answer

Alternator wont charge


at alternator gig wire battery voltage,one wire battery volts one less . battery volts wire goes to automatic shut down relay, less then battery voltage wire to pcm fuse will be 20 amp just ck all that size.

Aug 05, 2012 | 2001 GMC Sierra 2500HD

3 Answers

Got the codes checked and found the 52 code says


Most likely either battery or alternator. Also clean all the connections. If its an old battery I would change the battery first. Though if you take out the alternator it can be tested. If you have any other questions let me know.
thank you,
Lee

Nov 05, 2009 | 1993 Saturn SC1

1 Answer

What is the problem with keeping the battery charged? My new batteries only last less a year. The alternator checks out ok. Any ideas?


IT sounds like your problem is that you havent had your Alternator tested as what you have is over charging and the battery will be a 12 volt so the most itcan charge is 13.5 volts and yours is charging more (like 14 od 14.5 and thatsnot good) as what its doing is boiling the guts out of the battery and the water is like boiling a kettly it gets low till it runs out and then there is nothing to charge only DRY plates inside the battery. charging at 13.5 the battery will last about 3 years some times 5 or more.
Let me know how you go ,,,,Are you on Skype Ron

Oct 13, 2009 | 1995 Isuzu Rodeo

2 Answers

Battery voltage is very high when driving over 14


Voltage regulator is going bad. Have alternator tested or go ahead and have it replaced. Also this would be a good time to have the battery tested. Usually an alternator that is over charging will "cook" the battery causing it to not charge, not hold a charge, to losing the gel/electrolyte solution due to boil out.

Jul 17, 2009 | 2002 Audi A4

3 Answers

My battery is boiling and smelling. Is it a faulty battery, or is my alternator causing it to over-charge the battery?


You need to replace the battery to start with. you cannot test the charging system with the battery the way it is or you will get a false reading. Once you replace the battery, you can then test your charging system to see if the alternator is causing the problem. If its charging more than 14.8 -15 volts, its too much and you will need to replace the alternator.

Apr 13, 2009 | 1998 Honda Civic

1 Answer

Alternator when warm over charges 16 17 volts is regulator inside


are you boiling your battery?
are you having starting problem?
a shorted battery will cause you alt to charge very hard.

Sep 24, 2008 | 1988 Volkswagen Fox

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