Possible Causes & Corrections
WARNING: This page is about a different car, the 2003 GMC Sierra, 2003 GMC Cab & Chassis Sierra, 2003 Chevrolet Silverado, and 2003 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
Check for the following items:
- Ensure driver understands the Torque Converter Clutch (TCC) operation.
- Ensure driver understands the A/C compressor operation.
- Compare scan tool data at idle with scan tool data list. See PID VALUE CHARTS in PID VALUE CHARTS - SILVERADO & SIERRA article.
- Use scan tool to ensure the Vehicle Speed Sensor (VSS) reading matches the speedometer. This excludes vehicles with electronic transmissions where some variation between VSS and speedometer is normal.
- Inspect Fuel Rail Pressure (FRP) sensor. Observe FRP with scan tool. The FRP should be between 1.1-1.4 MPa. If not, inspect for high resistance in the FRP sensor circuits or FRP sensor.
- Test for an intermittent FRP sensor signal by wiggling harness between sensor and ECM with ignition on, and engine off, while monitoring the parameter with scan tool.
- Observe FRP sensor and fuel pressure regulator commanded percent at idle. FRP should be near 40 MPa, and commanded percent should be near 40 percent. If command is high, a fuel pressure or sensor problem exists.
- Inspect the Crankshaft Position (CKP) sensor reluctor wheel. Remove CKP sensor and attempt to move the reluctor wheel front to back or side-to-side with a probe. If there is any movement, the reluctor wheel retaining bolts are loose.
- Inspect fuel supply system pressure while the problem exists.
- Check for a sticking fuel pressure regulator. The symptom for this condition will be an idle surge of at least 100 RPM. This surge will be from 50 RPM above or below desired idle speed. See FUEL SYSTEM DIAGNOSIS - HIGH PRESSURE SIDE under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 6.6L SIERRA & SILVERADO - DIESEL article.
- Inspect the fuel injection control circuits between the ECM and Fuel Injection Control Module (FICM) for a short to a 5-volt reference circuit.
- Inspect control module grounds for being clean, tight, and in their proper locations.
- Inspect generator output voltage. Repair if voltage is less than 9 volts or more than 16 volts.
- Inspect Torque Converter Clutch (TCC) operation. See appropriate DIAGNOSIS article in AUTOMATIC TRANSMISSIONS.