Tech - Engine Misfire, Water in Fuel, SES Lamp Illum., DTC P0300 Set

Some drivers may comment about the Service Engine Soon lamp illuminating. The Powertrain Control Module (PCM) may have stored a Diagnostic Trouble Code (DTC) P0300, Engine Misfire Detected. The engine may be exhibiting a misfire, possibly in the #7 and #8 cylinders. This condition may also affect the six cylinder models. This condition may be more prevalent in areas with high amounts of rainfall.

Diagnosis of the fuel system may reveal the presence of water, possibly in the fuel rail near the #7 and #8 fuel injector. Water entering through the evaporative emission (EVAP) canister vent solenoid may cause this condition. Because of this, an engine misfire may develop.

A new EVAP canister vent hose assembly, P/N 15759042, that includes the valve and the solenoid has been developed to correct this condition. The new solenoid has a revised mounting bracket and a sealant has been applied to the top lid seal surface of the solenoid to address water intrusion. Use the procedure and the part numbers listed below.

If standard diagnostics do not lead to the resolution of the misfire, do the following steps:

1. Remove the fuel rail at the #7 and #8 fuel injector from the engine and drain the fuel into a suitable container. Inspect the drained fuel for the presence of water. Refer to the Fuel Rail Assembly Replacement procedure in the applicable Service Manual.
2. If the presence of water is detected in the fuel rail, remove the fuel tank and inspect the fuel for the presence of water. Refer to the Fuel Tank Replacement procedure in the applicable Service Manual.



3. If water is present in the fuel tank (other than from a water enriched fuel fill), replace the EVAP canister vent hose assembly. Refer to the EVAP Vent Valve Replacement procedure in the applicable Service Manual.
4. Disconnect the EVAP canister line connections and remove the canister. Inspect for the presence of water at the canister line connections and inside the canister. If water is present, replace the EVAP canister. Refer to the EVAP Canister Replacement procedure in the applicable Service Manual.
5. Flush and clean the fuel system. Refer to the Fuel System Cleaning procedure in the applicable Service Manual.

Parts are currently available from GMSPO.

For vehicles repaired under warranty, use: