Diagnostic Aids

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.

Inspect wiring for poor connections. Check for bent, backed out or damaged terminals, or poor terminal tension. Check for chafed wire or broken wire inside insulation. When diagnosing intermittent condition, wiggle wiring harness while watching scan tool for change in value.

Drive the vehicle if necessary to experience a fault.

If the condition is intermittent, connect the scan tool and select the speed sensor indicated by the code. If the signal is erratic, investigate and eliminate the following:

Intermittent wiring connection.
Excessive vibration (driveline or engine torsionals).
Irregular sensor gap (loose sensor, loose tone wheel, or damaged tone wheel).

Install a known-good speed sensor, and see if normal function is restored to rule out an internal short or open in the sensor removed.

Check that the speed sensor wiring consists of twisted pairs at the rate of 12 to 16 twists per 11.8" (300 mm). These twists must extend the entire length of the wiring harness to within at least 2" (50 mm) of the speed sensor connector.