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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.

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