← Back to list

P0131 and P0151 OBD2 Codes on 1997 Chevrolet Tahoe - Fuel Volume Issue Diagnosis

Model: 97 Tahoe Fault Code: P0131 Posted: 2009-01-10 09:52

I'm experiencing a recurring engine issue on my 1997 Chevrolet Tahoe with P0131 and P0151 diagnostic trouble codes. The engine runs smoothly at idle but dies and backfires when accelerated, indicating a lean condition. I've already checked fuel pressure (66 psi), which remains stable even after the engine is turned off. All key sensors—MAP, MAF, O2, and ECT—are reading within normal ranges. I performed a vacuum leak test using carb cleaner with no signs of leaks. I also verified ground connections for the VCM, O2 sensor harnesses, and exhaust system integrity. A restriction test on the exhaust showed no blockages. The engine has 128,000 miles, is not skipping, and injector balance tests are normal. Despite these checks, the vehicle exhibits a lean condition under load. I'm seeking expert insight into what might be causing this issue—especially given that the problem appears intermittent and resolves after a cold start or fuel change.

Related fault codes
P0131P0151
Comments (8)
Anonymous 2009-01-10 10:47

The symptoms suggest a potential fuel volume issue rather than just pressure. While fuel pressure may be within specifications, adequate flow rate is critical for proper air-fuel mixture delivery. I recommend checking the fuel filter first; if clean, consider replacing the fuel pump. Additionally, monitor the camshaft position sensor (CMP) PID to ensure it's reading correctly during operation.

Anonymous 2009-01-10 11:04

The fuel filter is confirmed clean with no blockages. The camshaft position sensor reads -6 degrees at idle and under load—within normal range. The vehicle runs fine when cold and in open-loop mode, indicating that fuel delivery is sufficient during warm-up. When the fuel pressure gauge was temporarily disconnected and the key turned on, fuel flow appeared adequate, further suggesting a volume issue rather than a pressure problem.

Anonymous 2009-01-10 16:43

What is the O2 sensor voltage when the engine begins to run lean? I expect it drops close to zero. What are the long-term and short-term fuel trim values? Does the calculated engine load exceed 80% at wide-open throttle (WOT)? If not, this could point to a dirty or faulty MAF sensor. Also, what is the dead-head fuel pressure under load?

Anonymous 2009-01-11 11:29

The O2 voltage drops into the teens when the engine runs lean. Long-term fuel trim is 1.6 at idle and 9.6 at WOT; short-term trim ranges from 7–8 at idle to 0 at WOT. Engine load reaches only 74% at WOT. I’ve tested a known-good MAF sensor from another 1997 Tahoe—no improvement. Dead-head fuel pressure is measured at 73 psi.

Anonymous 2009-01-11 17:26

I want to emphasize that if the exhaust system is clear and the MAF is functioning properly, a fuel volume issue remains the most likely cause. Even with optimal pressure, insufficient flow can lead to lean conditions. Another possibility is using E-85 fuel, which causes significant lean burn due to its higher octane and lower energy content. The open-to-closed loop transition may also be delayed—typically taking 2–3 minutes after a cold start.

Anonymous 2009-01-12 15:58

The vehicle reaches closed-loop mode after approximately 6 minutes of idling at ambient temperature (50°F). While I can't confirm E-85 use, the issue did appear about three weeks ago and then resolved—suggesting it may not be related to fuel type. This makes the problem even more puzzling. The vehicle is a real challenge—everything tested so far appears normal, but further diagnostics are still underway.

Anonymous 2009-01-14 15:40

After thorough testing, I've confirmed that it was indeed a faulty fuel pump with insufficient volume. A test on another 1997 Chevrolet truck revealed a significant difference in fuel flow—despite the original pump appearing visually intact. This confirms the root cause: inadequate fuel delivery under load. Thanks for the guidance, Asecmt.

Anonymous 2009-01-14 16:00

Great to hear you resolved it! This case highlights how even with normal pressure readings, fuel volume can be a hidden culprit in lean engine conditions on older vehicles like the 1997 Tahoe.