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Dave Nova
Dave Nova, Pontiac Technician
Category: Pontiac
Satisfied Customers: 19450
Experience:  ASE Master Certification. GM World Class Certification
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I am getting a po171 code. I have changed the o2 sensor before

Resolved Question:

I am getting a po171 code. I have changed the o2 sensor before the cat. It runs fine when it's warm,but sometimes it stalls when it's cold. The colder the temperature the more it wants to stall when it's cold. I have driven it 3 days now, about 300 miles, and the CEL has not illuminated yet. Any suggestions? It has been smoke tested for vacuum leaks and found to be tight.
Submitted: 6 years ago.
Category: Pontiac
Expert:  Dave Nova replied 6 years ago.
What model is your pontiac? What engine size?
Customer: replied 6 years ago.
It's a standard model, not a GT. Front wheel drive. 1.8Ltr. 4 cylinder. Vin#5Y2SL63845Z443727
Expert:  Dave Nova replied 6 years ago.

I have seen this issue several times before on the Vibe. The fix is to replace the PCM (powertrain control module) GM has published a technical service bulletin regarding this issue. I have included it below for your reference.


#PIP3621: DTCs P0171, P0441, and/or P2420 - Inspect Production Part Number on PCM - keywords CEL check ECM EVAP lamp lean light repeat trim updated - (Nov 9, 2005)

Subject:DTCs P0171, P0441, P0455 and/or P2420 - Inspect Production Part Number on PCM

Models:2005 Pontiac Vibe
with Automatic Transmission (RPO MU4)
and Base Front Wheel Drive (5th Digit of VIN = L)


The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.


On rare occasions, a check engine light may be experienced with DTC P0171, P0441, P0455, and/or P2420. These DTCs may be a result of an internal PCM driver issue that may keep the EVAP purge solenoid control circuit grounded at times instead of supplying a pulse width signal on the circuit.


If the SI diagnostics do not isolate a cause for the concern, inspect the white PCM label for any of the following part numbers, which may be causing the concern:

Toyota Production Part Number





GMSPO Service Part Number





If any of the above part numbers are found, replace the PCM with the correct one listed below:

Auto FWD with RPO JL4

Auto FWD without RPO JL4



Dave Nova and other Pontiac Specialists are ready to help you
Customer: replied 6 years ago.
where exactly is the PCM located physically on the vehicle?
Expert:  Dave Nova replied 6 years ago.

Behind the passenger side dash.


Object Number: 856534  Size: SH

  • Disconnect the battery. .
  • Remove the two retainers from the PCM close out panel (1) below the instrument panel (IP) glove box door.
  • Swing the PCM close out panel (1) down.
    Object Number: 834062  Size: SH

  • Open the glove compartment.
  • Push in on both sides of the glove compartment in order to release the safety catches.
  • Remove the glove compartment door assembly from the IP.
    Object Number: 834064  Size: SH

  • Remove the two PCM bracket fasteners.
    Object Number: 856535  Size: SH

  • Pull the PCM (2) with brackets (3) toward you and swing both down away from under the IP.
  • Disconnect the four PCM electrical connectors (1).
  • Remove the four fasteners and the two brackets (3) from the PCM (2).
  • After replacement of the PCM, the VIN must be programmed into the new PCM usint the dealers scan tool.