Diagnostic Aids

Perform this test when instructed during QUICK TEST, or when directed by other test procedures.

See HOW TO USE CIRCUIT TESTS under CIRCUIT TESTS before performing this test. Fuel contaminated engine oil may affect Codes 41/172, 91/136, 42/173 or 92/137. If this is suspected, remove PCV valve from valve cover and repeat QUICK TEST. If problem is corrected, change engine oil and filter.

Use this test to diagnose only the following components:

• HEGO sensor
• HEGO signal and ground circuit
• HEGO sensor connection
• Vacuum systems
• Fuel injector
• ECA
• Electrical circuits (HEGO GND, HEGO, INJ 1-8, VPWR and SIG RTN)

To prevent replacement of good components, be aware that the following non-EEC areas may be the cause of driveability concerns:

• Ignition coil, distributor cap or rotor
• Faulty or fouled spark plugs or wires
• Faulty CANP system
• Distributorless Ignition System (DIS)
• EGR valve and gasket
• Air filter
• Fuel or engine oil contamination
• Poor electrical ground
• Faulty fuel pressure
• Intake or exhaust system leaks
• Engine below normal operating temperature