2011 GMC Terrain Check Engine Light: U0109, P069E, and P0420 Codes - How to Fix & Clear for Registration
I own a 2011 GMC Terrain SLT with a persistent check engine light. I've spent over $900 on repairs without success, and I need the light to clear in order to register or sell the vehicle. The issue started when my dealer initially reported code U0109, which they attributed to a faulty fuel control module (FCM) — I paid $700 for replacement. After installation, the light turned off temporarily but returned within 15 minutes of driving home. A local electrician later identified three active codes: U0109, P069E, and P0420. He clarified that the fuel control module replaced by the dealer was not the correct component — it's a misidentification. The actual issue lies with the internal fuel pump module (FPM), which is located inside the fuel tank and connected directly to the fuel pump, not the external FCM in the rear of the vehicle. The car runs normally: starts easily, drives smoothly on highways and city roads, and has no noticeable driveability issues. The only anomaly I've noticed is a brief hesitation or power loss at around 28 mph when holding steady — it resolves immediately upon acceleration or deceleration. I'm seeking advice on the root cause of these codes and the most cost-effective way to clear the check engine light without spending hundreds more. Is this a wiring issue between the Powertrain Control Module (PCM) and Fuel Pump Control Module (FPCM)? Could it be a faulty connection, poor power/ground, or intermittent data communication? I'm also wondering if replacing the fuel pump module would resolve all codes — especially since P0420 suggests catalytic converter inefficiency. However, I understand that misfires or rich conditions typically cause this code, and my vehicle shows no such symptoms. Can anyone recommend a diagnostic approach (e.g., OBD2 scan tool, data logging) to identify whether the issue is electrical, mechanical, or related to module communication? And what steps should I take before replacing any parts?
Begin by checking power and ground connections for both the PCM and FPCM using an OBD2 scan tool. Use a data logger or scope to monitor CAN bus communication between the PCM and FPCM — intermittent faults are often due to wiring or connector issues. The fuel pump module (FPM) is not separate from the fuel pump; it's a single unit that includes both the pump and level sender, controlled by the FPCM. If the FPCM is malfunctioning, you should be able to communicate with it via scan tool — if there’s no communication, it points to a wiring or power/ground fault. There are no driveability symptoms reported? This suggests a non-critical issue but still needs diagnosis.