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ECM Computer Control Questions and Answers - This category
contains featured questions as examples. They relate to most vehicles.
Question: 1989 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: 1989 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: 1992 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: 1989 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: 1989 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.
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