Malfunction Indicator Light (MIL)
When ignition is first turned on, MIL should come on and remain on for 3 seconds to verify bulb and circuit operation, and then go off. The MIL is located in message center, above instrument panel.
The Powertrain Control Module (PCM) monitors several different engine control system circuits. If malfunction occurs which affects vehicle emissions, a Diagnostic Trouble Code (DTC) will be stored in PCM and PCM enters limp-in mode. When DTC is stored in PCM, the PCM will turn on the MIL and MIL will remain on steady.
If PCM detects active engine misfire severe enough to cause catalytic converter damage, MIL will flash to warn the driver of possible damage and DTC will be stored.
The PCM will turn off MIL when malfunction is not detected during 3 consecutive trips on all applications except an engine misfire or fuel system monitor.
Note. For additional information on engine misfire and fuel system monitor, see ON-BOARD DIAGNOSTICS.
The PCM will turn off MIL when malfunction is not detected during 3 engine misfire or fuel system monitor tests. The PCM performs engine misfire or fuel system monitor tests when engine is operating within 375 RPM and with 10 percent of the load of operating condition at which first malfunction was detected.
On-Board Diagnostics
The Powertrain Control Module (PCM) monitors several different engine control system circuits. If malfunction occurs, PCM will store a Diagnostic Trouble Code (DTC) when malfunction is detected, and PCM will enter limp-in mode. In limp-in mode, PCM substitutes values for failed component and provides continuous engine operation.
The PCM contains electronic circuit monitors that monitor fuel, vehicle emissions, engine and ignition system performance. Monitors use information from various sensor circuits for system monitoring. Monitors do not indicate a specific component failure, but do indicate an implied failure within a specified system, and that the problem must be diagnosed. If any monitor detects a problem affecting vehicle emissions, a Diagnostic Trouble Code (DTC) will be stored in PCM. The following monitors are used
- EGR Monitor
- Engine Misfire Monitor
- Fuel System Monitor
- Oxygen Sensor Monitor
- Oxygen Sensor Heater Monitor
- Catalyst Monitor
- EVAP System Leak Detection Monitor
The PCM will erase DTC once MIL is turned off. Once MIL is turned off, PCM must not detect the recent malfunction during 40 warm-up cycles on normal operation, or 80 warm-up cycles on engine misfire or fuel system monitor.
Note. A warm-up cycle is defined as the engine is started, an increase of 40°F (4°C) in engine coolant temperature exists after engine is started, and engine coolant temperature reaches at least 160°F (71°C).
The PCM also records and stores engine operating conditions when malfunction occurred. This information is referred to as freeze frame data. If malfunction is an engine misfire or fuel system rich or fuel system lean, freeze frame data will be updated with the most current information regarding these failures.
DTCs may be retrieved for system diagnosis. See RETRIEVING DIAGNOSTIC TROUBLE CODES under SELF-DIAGNOSTIC SYSTEM. System malfunctions are identified as either hard failures or intermittent failures.
Hard Failures
Hard failures cause MIL to illuminate and remain on until problem is repaired. If light comes on and remains on during vehicle operation, cause of malfunction must be determined by retrieving Diagnostic Trouble Codes (DTCs). See RETRIEVING DIAGNOSTIC TROUBLE CODES under SELF-DIAGNOSTIC SYSTEM. If a sensor fails, PCM will use substitute value in its calculations to continue engine operation. In this condition, commonly known as limp-in mode, the vehicle runs but driveability will not be optimum.
Intermittent Failures
Intermittent failures may cause MIL to flicker or illuminate and go out after intermittent failure goes away. However, the corresponding diagnostic trouble code will be retained in PCM memory. If related failure does not reoccur within a certain time frame, related diagnostic trouble code will be erased from PCM memory. Intermittent failures may be caused by a sensor, connector or wiring related problems. See INTERMITTENTS in TESTS W/O CODES - 3.0L article.
SERVICE PRECAUTIONS
Before proceeding with system diagnosis, following precautions must be followed
- Ensure fuel pressure is released before removing fuel line or fittings, as fuel system is under pressure and may cause personal injury.
- When using SELF-DIAGNOSTIC TESTS for diagnosis, DO NOT skip any steps or incorrect diagnosis may result. Always perform indicated verification procedure after repairs are made.
- When using a jumper wire, ensure either jumper wire or circuit is fuse-protected.
- Before disconnecting connector from any control module, ensure ignition is off before removing connector.
- When checking voltage or continuity at any control module, probe connector for control module from pin side. DO NOT backprobe connector or probe wires through the insulation.
- DO NOT cause short circuits when performing electrical tests. This will set additional Diagnostic Trouble Codes (DTCs), making diagnosis of original problem more difficult.
- Use specific test equipment as specified when performing electrical tests.
- When checking for spark, ensure coil wire is NOT more than 1/4" from engine ground. If coil wire is more than 1/4" from engine ground, damage to vehicle electronics and/or PCM may result.
- DO NOT prolong testing of fuel injectors or engine may hydrostatically lock.
- On models with 4-speed automatic transaxle, when replacing Transaxle Control Module (TCM), pinion factor, shift quality quick learn procedure and torque converter clutch break-in procedure should be performed. See PINION FACTOR PROCEDURE, SHIFT QUALITY QUICK LEARN PROCEDURE and TORQUE CONVERTER CLUTCH BREAK-IN PROCEDURE under COMPUTER RELEARN PROCEDURES in GENERAL INFORMATION.
Using Malfunction Indicator Light (MIL)
- Ensure battery is fully charged. Turn ignition on and note operation of MIL. The MIL is located in message center above instrument panel. When ignition is first turned on, MIL should come on and remain on for 3 seconds to verify bulb and circuit operation and then go off. NOTE: If MIL does not come on for 3 seconds and then go off, bulb circuit may be defective or problem area may exist on wire between between Powertrain Control Module (PCM) and instrument cluster.
- Attempt to start engine. Turn ignition off. Without starting engine, turn ignition on, off, on, off and on within 5 seconds. Record 2-digit Diagnostic Trouble Codes (DTCs) as displayed by flashing MIL.
- For example, DTC 24 will be displayed by 2 flashes, short pause and then 4 flashes. A short pause will exist between first and second digits on DTC. If more than one DTC is stored, after first DTC is displayed, there will be a longer pause and then another stored DTC will be displayed.
- Once all DTCs are recorded, proceed to retrieving DTCs using scan tool to ensure all DTCs are obtained. See USING SCAN TOOL.
Scheme 101
- Ensure battery is fully charged. Attempt to start engine. Turn ignition off. Connect scan tool to Data Link Connector (DLC) located below driver's side of instrument panel. (Scheme 101)
- Turn ignition on. Using scan tool manufacturer's instructions, record all DTCs displayed on scan tool. See SELF-DIAGNOSTIC TESTS DIRECTORY table. For additional information on retrieving DTCs, see DTC TEST under SELF-DIAGNOSTIC TESTS.
- Once all repairs are made, ensure DTCs are cleared from PCM. See CLEARING DIAGNOSTIC TROUBLE CODES under SELF-DIAGNOSTIC SYSTEM.
SUMMARY
If no diagnostic trouble code is present but driveability problem still exists, proceed to TESTS W/O CODES - 3.0L article for symptom diagnostic or intermittent diagnosis procedures.
FUEL PRESSURE RELEASE
| CAUTION | Fuel system is under high pressure. Release fuel pressure before disconnecting any fuel lines or fuel system components. |
| CAUTION | When battery is disconnected, vehicle computer and memory systems may lose memory data. Driveability problems may exist until computer systems have completed a relearn cycle. See COMPUTER RELEARN PROCEDURES article in GENERAL INFORMATION before disconnecting battery. |
- Disconnect connector at injector. Connect jumper wire between Dark Green/Orange wire electrical terminal on injector and positive battery terminal.
- Momentarily connect jumper wire between remaining electrical terminal on injector and ground for no longer than 5 seconds. DO NOT exceed 5 seconds or injector may be damaged. This operates injector and releases fuel pressure.
- Wait 5 seconds and then ground jumper wire for another 5 seconds. Remove jumper wires. Reinstall connector. Fuel pressure should now be released. Use care when disconnecting fuel lines, as some fuel pressure may still exist in fuel lines.