Diagnostic Aids

Inspect for the following conditions:

• Mass airflow (MAF) is compared to a calculated MAF based upon Manifold Absolute Pressure (MAP), Throttle Position (TP), and engine RPM readings. A skewed or unresponsive MAP sensor at KEY ON will cause predicted airflow value to be inaccurate. Compare MAP and TP sensor values to that of a known good vehicle.
• Faulty ECT sensor. Using a scan tool, compare engine coolant temperature with Intake Air Temperature (IAT) on a completely cool engine. ECT should be within 5°F (3°C) of intake air temperature. For an intermittent condition, go to INTERMITTENTS in TROUBLE SHOOTING - NO CODES - TRUCKS article.