Workshop Manuals Factory service & repair Chevrolet

Chevrolet common faults and how to fix them

Faults that are well known on Chevrolet models we hold manuals for: what the owner notices, what causes it, and the pages in our manuals that cover the repair.

Chevy P0171 and P0174: lean codes on the 5.3 V8 trucks and the Cobalt 2.4

Symptoms

The check engine light comes on with P0171 (fuel trim lean, bank 1) and often P0174 (bank 2). Some cars also log the P0300 random misfire code. Usually the engine runs normally, though some idle unevenly.

Cause

GM bulletins give three causes on the cars we hold manuals for. On 5.3 V8s with Active Fuel Management (2005–2006 Impala, Monte Carlo and TrailBlazer, and 2007 Avalanche, Suburban and Tahoe), injector connectors can be crossed, for example cylinder 6's plug on injector 8. On 2007–2008 trucks with vacuum brakes, a damaged or missing master cylinder seal at the brake booster lets in unmetered air. On the 2006–2007 Cobalt and HHR 2.4, the small director plates on the injectors clog up.

Fix

Smoke-test for vacuum leaks and check the mass airflow sensor first. Then check the bulletin for the car. On the AFM V8s, the Chevy P0171 bulletin says to check every injector connector is on the right injector, whatever the mileage. On 2007–2008 trucks, inspect the P0174 Chevy brake booster seal. On the Cobalt, run an injector balance test: the bulletin warns that cleaning won't clear the director plates, so faulty injectors are replaced.

Repair instructions on this site

Sources: GM service bulletins 06-06-04-001A and 08-06-04-001B; GM bulletin on P0171/P0174 and the brake master cylinder seal.

Chevy P0300: rough idle and misfire on the 4.8, 5.3 and 6.0 V8 (2002–2004)

Symptoms

A rough idle and misfires, with the check engine light on and P0300 (random misfire) stored. It is worst on the 5.3 flex-fuel engine, but the same fault can occur on regular-fuel 4.8, 5.3 and 6.0 Vortec V8s in the Silverado, Suburban, Tahoe and Avalanche.

Cause

GM bulletin 05-06-04-029A traces it to the upper intake manifold gaskets. On the flex-fuel 5.3 (L59), the engine computer delivers more fuel for ethanol, and the fuel can pool on the gasket material between the manifold and the heads. The fix is a revised gasket material that copes with it.

Fix

Start with the normal misfire checks: plugs, coils and leads, and a smoke test for intake leaks. If the intake gaskets are leaking, the Chevy P0300 bulletin replaces them with the teal green gasket material, part number 89017589. Do not refit the original orange gaskets (17113557). The same Silverado P0300 repair applies across the 2002–2004 trucks.

Repair instructions on this site

Sources: GM service bulletin 05-06-04-029A.

Chevy knock sensor: P0332, spark knock on the 4.8, 5.3, 6.0 and LS1 (1998–2002)

Symptoms

A mild to severe pinging (spark knock), usually worse under acceleration, and the check engine light on with P0332 (knock sensor 2 circuit).

Cause

GM bulletin 02-06-04-023A says water gets into the cavity under the intake manifold where the rear knock sensor sits, and corrodes the sensor. It is more common on trucks whose engine bay is often washed. It covers the 1999–2002 Silverado, Suburban and Tahoe, the 2002 Avalanche, and the 1998–2002 Camaro and Corvette with the LS1.

Fix

The knock sensors sit under the intake manifold, so the manifold has to come off. The Chevy knock sensor bulletin replaces the rear sensor and builds a dam of RTV sealant around it to keep water away. Check the wiring to both sensors while the manifold is off, and fit new intake gaskets. The Silverado knock sensor job is the same on the trucks and SUVs.

Repair instructions on this site

Sources: GM service bulletin 02-06-04-023A.

Chevy P0455 and P0446: EVAP vent valve on the Tahoe, Suburban and Avalanche (2007–2010)

Symptoms

The check engine light comes on with EVAP codes P0442, P0446, P0449 or P0455, and the fuel tank may be hard to fill, with the pump clicking off early.

Cause

GM bulletin 09-06-04-028C covers the 2007–2010 Avalanche, Suburban 1500 and Tahoe (and their GMC and Cadillac twins). The EVAP canister vent solenoid draws fresh air through a vent attached to the fuel filler pipe. Water gets into the vent valve, so it sticks or fails, giving the codes and the slow filling.

Fix

Read the codes and check the vent valve for water. The Chevy P0455 bulletin fits a revised canister vent solenoid valve, which comes with two tie-straps to fix its vent pipe to the fuel filler pipe as the bulletin shows. Clear the codes and confirm the EVAP tests pass on a later drive. A loose fuel cap gives similar codes, so check that too.

Repair instructions on this site

Sources: GM service bulletin 09-06-04-028C.

Repair instructions for every Chevrolet model: Chevrolet workshop manuals