Scan Tester
Trouble codes are retrieved from EEC system through Data Link Connector (DLC), located behind left side of instrument panel below fuse/relay panel. (Scheme 22) Follow scan tester manufacturer's instructions to retrieve codes.
Malfunction Indicator Light (MIL)
Trouble codes are retrieved from EEC system through MIL (CHECK ENGINE light) located on instrument panel. MIL is used with Diagnostic Test Connector (DTC) located near starter motor. (Scheme 22). To retrieve codes, use the following procedure
- Turn ignition key to ON position. Disconnect the diagnostic connector in engine compartment. Jumper terminals as indicated in illustration, and wait 2 seconds. (Scheme 22).
- Remove jumper wire and reconnect diagnostic connector. Record DTC, MIL flashes.
READING CODES
All trouble codes are 2-digit numbers. PCM outputs codes one digit at a time. These codes indicate current faults in system and should be serviced in order of appearance. See TROUBLE CODE REFERENCE under CIRCUIT TESTS to find correct CIRCUIT TEST.
Scan tester, if used, will count pulses and display them as a digital code. If using MIL, trouble codes are displayed as light pulses from CHECK ENGINE light. When using MIL, pay attention to length of pauses in order to read codes correctly. (Scheme 21)
Pass Codes
Code 55 indicates system passes that portion of test. If Code 55 is not retrieved, proceed to CIRCUIT TEST corresponding with trouble code that is output.
Scheme 21
CLEARING CODES
To clear codes from PCM memory when using MIL (CHECK ENGINE light), disconnect jumper wire and reconnect harness connectors. If using scan tester, follow tool manufacturer's instructions. If problem has not been corrected or fault is still present, code will immediately be reset in PCM memory.
VISUAL CHECK & EQUIPMENT HOOKUP
Complete all steps in BASIC TESTING - 3.0L article before proceeding to self-diagnostic tests. Ensure vacuum hoses and wiring harnesses are properly connected. Apply parking brake, and place shift lever in Park (A/T) or Neutral (M/T). Block drive wheels. Turn off all electrical loads. Connect appropriate test equipment to vehicle as follows
Note. To retrieve codes using the MIL, see MALFUNCTION INDICATOR LIGHT (MIL) .
Turn ignition switch to OFF position. Hook up equipment to Data Link Connector (DLC), located behind left side of instrument panel, below fuse/relay panel. (Scheme 22) Follow manufacturer's instructions, and record trouble codes.
Scheme 22
ADDITIONAL SYSTEM FUNCTIONS
Additional diagnostic system features are available to help diagnose driveability problems and service EEC systems.
MIL
MIL is CHECK ENGINE light on instrument panel. MIL is intended to alert driver of certain malfunctions in EEC system. Light may also be used to retrieve trouble codes stored in PCM. When hooked up for KOEO SELF-TEST, light will display all codes which turn on light during vehicle operation.
If light comes on during vehicle operation, vehicle should be inspected as soon as possible. Immediately turning off engine is not necessary. Vehicle can be driven with light on. On California models, MIL will come on and stay on if a system monitored by PCM malfunctions. On Federal models, MIL will stay on only if PCM or Camshaft Position (CMP) sensor malfunctions.
CIRCUIT TESTS
Note. A breakout box, connected to vehicle harness at PCM, is necessary to perform most circuit tests. References to test pin numbers in CIRCUIT TEST steps refer to test terminals on manufacturer breakout box overlay. Circuit diagrams and tables at beginning of each test identify circuits and wire colors.
HOW TO USE CIRCUIT TESTS
1) Ensure all non-EEC related faults found while performing steps in BASIC TESTING - 3.0L article have been corrected. Follow each test step in order until fault is found. When more than one code is retrieved, start with first code displayed.
2) CIRCUIT TESTS ensure electrical circuits are okay before sensors or other components are replaced. Always test circuits for continuity between sensor and PCM. Test all circuits for short to power, opens, or short to ground. Voltage Reference (VREF) and Voltage Power (VPWR) circuits should be tested with ignition on unless otherwise specified in CIRCUIT TESTS.
3) DO NOT measure voltage or resistance at PCM. DO NOT connect any test light unless specified in testing procedure. All measurements are made by probing rear of connector. Isolate both ends of a circuit and turn ignition off when checking continuity.
4) Disconnect solenoids and switches from harness before measuring continuity and resistance or applying voltage. After each repair, reconnect all component connections and repeat QUICK TEST.
5) An open circuit is defined as a resistance reading of greater than 5 ohms. This specification tolerance may be too much for some items in EEC system. If resistance approaches 5 ohms, always clean suspect connector and coat it with protective dielectric silicone grease. A short is defined as a resistance reading of less than 10,000 ohms to ground, unless stated otherwise in CIRCUIT TEST.