Diagnostic Aids
WARNING: This page is about a different car, the 2003 Pontiac Grand Am, 2003 Oldsmobile Alero, 2003 Chevrolet Monte Carlo, and 2003 Chevrolet Impala. However, it is still accessible from the selected car via links, so may be relevant.
- A vacuum restriction to the MAP sensor. A skewed MAP sensor reading can cause the PCM to read incorrect MAP changes during the EGR flow test.
- An engine that is running poorly due to a mechanical condition such as worn piston rings, worn camshaft, etc. These types of conditions can cause low engine vacuum and thus can cause a less than expected MAP changes during the flow test.
- Exhaust system leaks can cause an insufficient amount of EGR flow through the EGR valve. This condition can cause a less than expected MAP changes due to insufficient exhaust back pressure. Possible causes of this could be a leaking exhaust system, a leaking EGR pipe or non Original Equipment Manufacture (OEM) exhaust parts.
- A restriction in the intake manifold such as carbon deposits and casting flash.