Ok, I have a couple of bulletins for you to check out.
|Subject:||Cold Engine Idle Misfire or DTCs P0171 P0174|
|Models:||2002-2005 Cadillac Escalade|
|1999-2005 Chevrolet Avalanche, Express, Silverado, Suburban, Tahoe, Trailblazer|
|1999-2005 GMC Savana, Sierra, Yukon|
This PI was superseded to update parts information. Please discard PIP3232A.
The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.
99 through 05 GEN III truck engines may experience any of the following:
- A cold rough idle that diminishes as the engine warms up.
- Possible DTCS P0171, P0174, or P0300.
- Random misfires at idle.
The intake gasket seals may be leaking around the intake ports, causing a lean condition. The intake gasket seals may leak around the bottom side of the port, making it a challenge to detect the vacuum leak. The technician may also notice lower than normal MAF readings if the intake seals are leaking.
- If leaking intake gasket seals are found, replace the intake gaskets. During the repair be sure to use the current GMSPO part number for replacement intake gaskets. The current GMSPO part number for intake gaskets will have a teal green intake gasket seal. The old version of the intake gaskets were orange in color. Use only the teal green colored gaskets for a repair.
- The intake plenum should also be checked for excessive warpage that may cause an uneven clamping pressure of the seal. If the plenum is found to be warped it will need to be replaced. Service Information states, "An intake manifold with warpage in excess of 3 mm (0.118 in) over a 200 mm (7.87 in) area should be replaced". Intake warpage is measured at the gasket sealing surfaces, and should be measured within a 200 mm (7.87 in) area. This measurement is across only two of the intake runner port openings. Measurements taken across the entire distance of all four intake runner ports will lead to unnecessary manifold replacements.
Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.
|Subject:||LM7, L59 or L33 Engines with Cold Start Rough or Incorrect Idle, Misfire, Malfunction Indicator Lamp (MIL) or Flashing Requiring O2 Sensor Replacement (Reprogram PCM)|
|Models:||2004-2005 Cadillac Escalade|
|2004-2005 Chevrolet Avalanche, Silverado 1500, Suburban, Tahoe|
|2005 Chevrolet Silverado Hybrid (HP2)|
|2004-2005 GMC Sierra 1500, Yukon, Yukon XL|
|2005 GMC Sierra Hybrid (PH2)|
|with Vortec 5300 5.3L V-8 Engine (VINs T, Z, B -- RPOs LM7, L59, L33)|
Some customers may comment on a Malfunction Indicator Lamp (MIL) On or that the MIL is flashing. An actual engine misfire may or may not be felt along with an incorrect idle speed. Typically this occurs during cold winter months, on cold engine starts. Some vehicles may have been previously serviced for the same condition. Technicians may also find the following DTCs stored with the Tech 2® P0131, P0133, P0134, P0137, P0138, P0140, P0151, P0153, P0154, P0157, P1133, which may be in conjunction with P0171, P0174, P0300 and P1138.
Water shock occurs when water droplets are present in the exhaust. The water in the exhaust contacts the sensor element inside the HO2 sensor, causing the HO2 sensor element to crack.
Upon diagnostic investigation, the technician may find that the HO2 sensor requires replacement. In addition to replacing the affected HO2 sensor, these vehicles should also be reflashed with the latest PCM calibration. An updated PCM calibration will be available to dealerships as part of TIS 2000 incremental satellite update 11.0 (NAO version 25.010) or greater. Always, make sure your Tech 2 is updated with the latest software version.
Important: If a DTC P0420 or P0430 is stored along with DTC(s) P0300, the catalytic converter diagnostics in Service Information (SI) must be followed to determine if the catalytic converters are operating properly.