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2003 GMC Envoy SLT P0172 and P0756: Sluggish Engine Power, Overdrive Slip in Hot Weather

Model: 2003 gmc envoy SLT Fault Code: P0172 Posted: 2008-08-20 16:52

Hi everyone, I recently had a friend ask to use my 2003 GMC Envoy SLT to pull a boat. During the trip, the engine lost power—became sluggish and unresponsive when fully accelerating. The vehicle feels weak under load, especially in gears 2 through 4. After the drive, I noticed this issue persists across all gears. I used an OBD2 scanner (CP9180) and initially detected two trouble codes: P0172 and P0756. After clearing the codes, the symptoms remain, but only P0172 returns consistently. I’ve researched these codes extensively and found helpful information, but I’m concerned about how extensive repairs might be. I suspect the issue could involve multiple systems—fuel delivery, emissions, or transmission—but I’d like to narrow down the possibilities before committing to major work. The engine is a 4.2L inline-6, 4-wheel drive, and I live in Palm Desert, CA, where daily temperatures reach up to 110°F. The vehicle often feels like it's slipping into overdrive too early—especially when warmed up—which causes a loss of power. If I accelerate gently and avoid overdrive, it can maintain speed. But if I let the transmission engage overdrive or drive for extended periods, the engine becomes completely unresponsive and requires me to stop and idle for 5–18 minutes before regaining performance. I’m not very experienced with OBD2 diagnostics but am willing to provide readings from my scanner if needed. Could anyone recommend a troubleshooting flow for this specific combination of P0172 and P0756 on a 2003 GMC Envoy SLT? What are the most likely root causes, especially in hot weather conditions? Thanks in advance!

Related fault codes

P0172P0756

Comments (3)

Anonymous 2008-08-21 05:22

You're seeing two codes—P0172 and P0756—which may point to two separate issues. Could you check the transmission fluid condition? Is it clean, or does it appear slightly thick? Also, which engine model are you running in your Envoy?

Anonymous 2008-08-23 12:20

Hi Jeff—thanks for the reply! The transmission fluid looks clean but might be a bit thicker than ideal. I'm not sure if that's affecting performance. The engine power and responsiveness have significantly degraded over the last few days, especially in hot weather. I live in Palm Desert, CA, where temperatures regularly hit 110°F. The engine is a 4.2L inline-6 with 4-wheel drive. I’ve tested it multiple times and now only see P0756 consistently. When driving, the vehicle tends to shift into overdrive too early—especially during takeoff—and feels like it's slipping. If I accelerate slowly and avoid overdrive, it eventually reaches speed. But if I let it go into overdrive or drive for a while, especially when warm, there’s no power at all. I have to stop and idle for 5–18 minutes before the engine regains responsiveness. I can provide OBD2 readings from my scanner if helpful. However, I’m new to diagnostics—what parameters should I be checking? What are typical values for fuel trim, transmission shift points, or other key metrics? I plan to perform a full engine inspection tomorrow morning to rule out common issues step-by-step.

Anonymous 2008-08-24 11:46

Older Envoy models were known to have catalytic converter clogging issues that could cause sluggish performance, but P0172 and P0756 don’t typically point directly to that. I’d recommend having a certified dealer or a reputable transmission specialist inspect the vehicle. While some issues may be fixable at home, transmission problems are rarely DIY-friendly—especially when they involve shifting behavior and power loss under load.