Repair Topics / ECM Computer

ECM Computer Control Questions and Answers

This category contains featured questions as examples. They relate to most vehicles.

Question: 1999 Olds Cutlass Cierra mileage: 82,000.  My problem is the ECM fuse keeps blowing; sometimes it may last 5 minutes and then other times it may blow with the switch being turned on the crank mode.   Do you have any suggestion that may help me?

Answer:  Check the wiring loom for damage or to see if it is shorted out.   In addition, you may possibly have a bad PCM (power control module), which is the same thing as an ECM.

Question: 2002 Oldsmobile Cierra mileage: 102,000.  The ignition key wore out such that the ignition tumbler would not turn off. To shut the vehicle off, I pulled the ignition and ECM fuses.  I then disconnected the battery. I purchased a new ignition tumbler and replaced it in the column.  I grounded the positive side of the battery to clear the ECM memory.  Reconnected both battery terminals and tried to start the car.  The engine would crank but not turn over; I removed one plug to check for spark, which was not present.  I checked for error codes and only got code 12, which means no RPM.  Before this, I never had a problem starting the car and suspect that I may have damaged the ECM.  How can I verify this and where is the module located in my car?

Answer:  The correct way to clear the ECM on your model car is to disconnect the negative battery cable and after 30 seconds, re-attach.  They procedure you used may have damaged the ECM.  This can be verified by replacing the ECM with a known good unit.  The ECM is located behind the glove box - passenger side.  Also check for 12-volts to the ECM.

Question: 2002 GMC S15 mileage: 95,000.  Having repeating problem with ECM.  Engine check light comes on.  Engine runs so rough cannot drive.  Original problem occurred driving 60 mph on freeway, engine light came on, lost power but made it 10 miles home.  The computer code is always 2-3 (mixture control solenoid).  Over last 5 months, have replaced: mixture control solenoid, oxygen sensor, ECM (3 times), entire carburetor, added ground wire from ECM to firewall & engine to firewall.  Has been to a local shop and to a Chevy dealer.  The truck has a remanufactured long block with about 5,000 miles on it.  New fuel and water pumps were installed at engine replacement.  Within last 8 months alternator, starter, and battery were replaced.  Truck still does not run reliably.  ECMs have been lasting 3 to 30 days.  I tried to find a replacement wiring harness and its not available from dealer.  Any suggestions?   I have lost faith in local dealer & repair shop.  Roy

Answer:   What comes to mind is AC voltage from the alternator from a leaking diode, or high voltage (from the coil) somehow is getting back down the wiring harness to the ECM or bad plug wires next to a wiring loom or stray high voltage in the distributor getting into low voltage wiring.

Question: 1999 Pontiac Grand Am mileage: 100,000.  I need help! I have been working on this car on and off for one month.  This is what I have done: Symptoms: The car intermittingly raises the idle on its own to 2500 rpm.   I have code scanned and code 35 comes up.   This means a problem with the IAC control valve.  I have replaced the IAC and the throttle position sensor and the 02 sensor and the code still comes up.   (service soon light on).  I have recently invested in an Actron Tech Tool, which has been helpful, but I am not sure with my conclusion.  I have replaced the battery also because it was leaking acid at the terminal connections which I thought could cause the computer to not function correctly, hence problem solved.  Battery did not solve the problem.  (I did clean all the acid from the terminals)  I have checked the battery when the car is running with the tech tool and the voltage is dropping to 6 to 7 volts on the tech tool screen. 

 I checked the voltage from the battery to the ECM and it is 12.5 volts on both orange wires running to the ECM.  As soon as the car drops to the 6 volts the IAC reading goes up to 255 on the tech tool.  Then all by itself the car will start to idle normal at 1025 RPM and the voltage will read 13.5 volts (running).  At this point, the IAC will be at 28.  (Which I believe is normal).  I will shut the car off and start it again and the voltage on the tech tool will be back at 6 volts.  I think that the ECM itself is intermittingly showing the wrong voltage, which is causing the IAC to go out of control limits, and causing the idle to rise to 2500 RPM.  I even double-checked over and over to make sure that the voltage going into the ECM is staying at 12.6 volts.  Please help me.   I am thinking of getting another ECM but they are expensive.  I would like to hear from you before I make this purchase.

Answer:   From what you describe and have checked, we would think the ECM is the problem.  Additionally, if you replace the ECM, also replace the calibration prom.

Question: 1999 Chevy Lumina mileage: 104,000.  Can I remove the ECM and have it tested.  After cleaning fuel system, replacing a plugged fuel filter and testing the fuel pump and pressure, the injectors appear not to be firing.  I've got good spark and 40# fuel pressure at the rail. Upon removing plugs, they are dry.  No codes appear.   The car just started bogging down and then would barely run with no power and then just quit.  It has done that several times and now won't start at all.

Answer:  We do not know of any service to "test" an ECM.   We would suggest substituting it for a known good unit.  Also, check the power supply to the ECM and ground connections.

Repair Topics / ECM Computer

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