"PCM needs replacement" mechanic claims. [Archive] - GrandAmGT.com Forum

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Shad0wguy
03-17-2007, 06:44 AM
Heres the story folks.

Last year I had my LIM replaced. Once I got the GA back I started getting 2 codes that indicated a bad IAT sensor. I brought the GA back a few months later and they refused to fix it, claiming it was caused by my CAI, which wasn't even installed until after the issue began.

Now, about a year later, the time for inspection has passed. I had brought it to a new mechanic who scanned it and found a new code. So now I have 2 IAT codes and 1 MAP code. He is claiming that the PCM is sending incorrect voltages and needs replacement.

I have already tried replacing the sensors that are throwing the codes and then clearing the codes, but they come back after a few minutes.

These are the codes...

P0113B IAT sensor circuit high voltage
P1106C MAP sensor intermittent high voltage
P1111C IAT sensor circuit intermittent high voltage

Do you believe that replacing the PCM is the right thing to do, or can you think of other things that may be causing it? And where can I get a used PCM for cheap? My local salvage yard quoted $125. Is that the normal price?

lvemy3100
03-17-2007, 06:59 AM
DTC P0113 Intake Air Temperature (IAT) Sensor Circuit High Voltage

The Intake Air Temperature (IAT) sensor is a thermistor which measures the temperature of the air entering the engine. The PCM applies 5V through a pull up resistor to the IAT sensor. When the intake air is cold, the sensor resistance is high and the PCM will monitor a high signal voltage on the IAT signal circuit. If the intake air is warm, the sensor resistance is lower causing the PCM to monitor a lower voltage. DTC P0113 will set when the PCM detects an excessively high signal voltage on the intake air temperature sensor signal circuit.

Conditions for Setting the DTC
No active ECT sensor or VSS DTC present.
Vehicle speed is less than 35 mph.
Mass Air Flow is less than 12 gm/s.
Engine Coolant Temperature is greater than 60C (140F).
IAT signal voltage indicates an intake air temperature less than -37C (-34F).
The above conditions are present for at least 3 minutes.
Action Taken When the DTC Sets
The PCM will illuminate the malfunction indicator lamp (MIL) during the second consecutive trip in which the diagnostic test has been run and failed.
The PCM will store conditions which were present when the DTC set as Freeze Frame/Failure Records data.
Conditions for Clearing the MIL/DTC
The PCM will turn OFF the malfunction indicator lamp (MIL) during the third consecutive trip in which the diagnostic has run and passed.
The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
The DTC can be cleared by using a scan tool.
Diagnostic Aids
Check for the following conditions:

Poor connection at PCM. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection.
Damaged harness. Inspect the wiring harness for damage. If the harness appears to be OK, observe the IAT display on the scan tool while moving connectors and wiring harnesses related to the IAT sensor. A change in the IAT display will indicate the location of the fault.
The Temperature vs. Resistance table may be used to test the IAT sensor at various temperatures to evaluate the possibilitiy of a shift sensor that may be open above or below a certain temperature. Refer to Temperature vs Resistance . If this is the case, replace the IAT sensor. Refer to Intake Air Temperature (IAT) Sensor Replacement . If the IAT sensor appears to be OK, the fault is intermittent. Refer to Diagnostic Aids.
If DTC P0113 cannot be duplicated, the information included in the Fail Records data can be useful in determining vehicle mileage since the DTC was last set.

Test Description
The numbers below refer to the step numbers on the Diagnostic Table:

Verifies that the fault is present.

If DTC P0113 can be repeated only by duplicating the Fail Records conditions.

This vehicle is equipped with a PCM which utilizes an Electrically Erasable Programmable Read Only Memory (EEPROM). When the PCM is being replaced, the new PCM must be programmed.


DTC P1106 Manifold Absolute Pressure (MAP) Sensor Circuit Intermittent High Voltage

The Manifold Absolute Pressure (MAP) sensor responds to changes in intake manifold pressure (vacuum). The MAP sensor signal voltage to the PCM varies from below 2 volts at idle (high vacuum) to above 4 volts with the key ON, engine not running or at wide open throttle (low vacuum).

The MAP sensor is used to determine manifold pressure changes while the linear EGR flow test diagnostic is being run (refer to DTC P0401), to determine engine vacuum level for some other diagnostics and to determine barometric pressure (BARO). The PCM monitors the MAP signal for voltages outside the normal range of the MAP sensor. If the PCM detects a MAP signal voltage that is intermittently high, DTC P1106 will be set.

Conditions for Setting the DTC
No TP sensor DTC(s) are present.
Ignition ON.
Throttle angle is steady below 2% if engine speed is below 3000 RPM.
Throttle angle is steady below 30% if engine speed is above 3000 RPM.
The MAP sensor indicates an intermittent manifold absolute pressure above 90 kPa.
Above conditions for over 10 seconds.
Action Taken When the DTC Sets
The PCM stores conditions which were present when the DTC set as Failure Records only. This information will not be stored as Freeze Frame Records.

Conditions for Clearing the MIL/DTC
The DTC becomes history when the conditions for setting the DTC are no longer present.
The history DTC clears after 40 malfunction free warm-up cycles.
The PCM receives a clear code command from the scan tool.


DTC P1111 Intake Air Temperature (IAT) Sensor Circuit Intermittent High Voltage

Circuit Description
The Intake Air Temperature (IAT) sensor is a thermistor which measures the temperature of the air entering the engine. The PCM applies 5 volts through a pull up resistor to the IAT sensor. When the intake air is cold, the sensor resistance is high and the PCM will monitor a high signal voltage on the IAT signal circuit. If the intake air is warm, the sensor resistance is lower causing the PCM to monitor a lower voltage. DTC P1111 will set when the PCM detects an intermittently high signal voltage on the intake air temperature sensor signal circuit.

Conditions for Setting the DTC
No VSS, ECT, or MAF DTCs present.
Vehicle speed is less than 35 mph.
IAT signal voltage indicates an intake air temperature intermittently less than -39C (-38F).
The above conditions are present for up to 3 minutes.
Action Taken When the DTC Sets
The PCM stores conditions which were present when the DTC set as Failure Records only. This information will not be stored as Freeze Frame Records.

Conditions for Clearing the MIL/DTC
The DTC becomes history when the conditions for setting the DTC are no longer present.
The history DTC clears after 40 malfunction free warm-up cycles.
The PCM receives a clear code command from the scan tool.
Diagnostic Aids
Check for the following conditions:

Poor connection at PCM. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection.
Damaged harness. Inspect the wiring harness for damage. If the harness appears to be OK, observe the IAT display on the scan tool while moving connectors and wiring harnesses related to the IAT sensor. A change in the IAT display will indicate the location of the fault.
Reviewing the Fail Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused the DTC to be set occurs. This may assist in diagnosing the condition.





HTH...

Shad0wguy
03-17-2007, 11:09 AM
Wow, thats a lot of info.

Like I said, I replaced the IAT sensor with the same result. My mechanic said the IAT was reading at -35*.

The only thing I have noticed that may be causing it it some rusting on the wires going to the harness. Maybe that is causing more resistance and, in turn, causing the SES.

drumking1721
03-17-2007, 11:13 AM
^^^ He knows his shiiizzzz

lvemy3100
03-17-2007, 12:25 PM
below I have quoted what you should look for... from my original post above...

.....
[B]Check for the following conditions:

Poor connection at PCM. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection.
Damaged harness. Inspect the wiring harness for damage. If the harness appears to be OK, observe the IAT display on the scan tool while moving connectors and wiring harnesses related to the IAT sensor. A change in the IAT display will indicate the location of the fault.
The Temperature vs. Resistance table may be used to test the IAT sensor at various temperatures to evaluate the possibilitiy of a shift sensor that may be open above or below a certain temperature. Refer to Temperature vs Resistance . If this is the case, replace the IAT sensor. Refer to Intake Air Temperature (IAT) Sensor Replacement . If the IAT sensor appears to be OK, the fault is intermittent. Refer to Diagnostic Aids.
If DTC P0113 cannot be duplicated, the information included in the Fail Records data can be useful in determining vehicle mileage since the DTC was last set.

.....
Poor connection at PCM. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection.
Damaged harness. Inspect the wiring harness for damage. If the harness appears to be OK, observe the IAT display on the scan tool while moving connectors and wiring harnesses related to the IAT sensor. A change in the IAT display will indicate the location of the fault.
Reviewing the Fail Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused the DTC to be set occurs. This may assist in diagnosing the condition. .....




..

gectek
03-18-2007, 03:26 PM
i would def look at the harness before looking at the pcm for it being bad. those harnesses prob have a common ground point, which does look to be inside the PCM... they are both given a reference voltage and then they send back a voltage in return due to induced resistance in the sensor. then the circuit is grounded by the PCM. so then u should check all the wiring harnesses from both sensors, and when u unplug them check for any resistance in the individual wire from one end of the wire to the other. also check for shorts across the 2 wires. u may have to make leads because the pcm is inside the car and the sensors are under the hood, but its a good way to check. also when u plug the connectors back in the sensors, make sure to use dielectric grease to make sure the connections are good.

also the computer grounds through 4 diff wires on a spice pack at the front of the engine on the trans mount by the alternator. make sure all those wires are ok and that the ground is in good shape. also clean the place where the ground meets and the grounding tab on the splice pack. just a few places to start. but if it is not that, then u need to replace the PCM

Shad0wguy
03-20-2007, 06:23 AM
Does anyone have a diagram of the wire harness? I need to know what wires I should check for the sensors that are malfunctioning.

gectek
03-20-2007, 01:27 PM
pinouts of conns and the wiring diagram...they all go from PCM to PCM though...

Shad0wguy
03-21-2007, 06:37 AM
they all go from PCM to PCM though...

Thanks. But what do you mean by that.^

gectek
03-21-2007, 10:16 AM
i mean that all the wires go from the PCM back to the PCM, none of them are run to an ouside ground. so it would either be at the PCM, the sensor, or the harness

Shad0wguy
03-22-2007, 06:12 AM
oh, ok. I understand.

digitalballz
03-22-2007, 07:44 PM
Why does everyone always doubt the mechanic?

Shad0wguy
03-22-2007, 08:44 PM
Cause they usually tell you whatever makes them the most money. They don't expect anyone to know any better.

gectek
03-23-2007, 05:16 PM
well not everyone tries to screw you. but also it may very well be the pcm

Shad0wguy
03-24-2007, 05:30 AM
I know that he may be right. But thats why I'd like to test first. I don't want to spend the money if it isn't the issue.

Shad0wguy
04-01-2007, 01:56 PM
I need to bump this thread.

I tested the wiring going to the IAT and got no voltage readings. And in the process the black wire split. I cannot get enough slack to re-solder the wire.

Does anyone know where I can get a new IAT harness, or should I just get one from a salvage yard?

gectek
04-01-2007, 10:13 PM
you can get a brand new pig tail from GM...i can price one for u if you want. i would def not get anything elec from a JY