Engine Controls - Tests W/codes: Other Isuzu Trooper II

TRIP DETECTION LOGIC

Generation II data streams are prioritized. When two messages attempt to establish communications on a data line at the same time, only the message with higher priority will continue. A new segment of the software called the Diagnostic Executive coordinates the protocol for recording and displaying diagnostic procedures.

After engine has reached normal operating temperature, Diagnostic Executive checks if On Board Diagnostic Tests have been completed since last ignition cycle. It checks if tests have passed during current ignition cycle. Checks if fault identified by diagnostic tests is currently active. It also checks if fault identified has been active during current ignition cycle and what operating conditions were present at the time of failure.

Each test is separated in to four types

1. Type A Turns the MIL on the first time an emission related failure occurs. The MIL will FLASH at a rate of once per second to alert the operator of potentially damaging levels of misfire, such that could destroy the catalytic converter.
2. Type B Will only turn MIL on if an emission related condition occurs during two consecutive driving cycles. Conditions such as incorrect fuel trim will be stored in the Freez-Frame data until the fault is detected a second time. If the fault is not detected during three consecutive driving cycles, the MIL light will be turned off.
3. Type C This is a non-emission related type and will not activate the MIL. It will turn ON a Check Transmission service light, or other non MIL service reminder light.
4. Type D Is non-emission related, will not turn the MIL or service light, but will store DTCs of faults present.

HARD FAILURES

Hard failures cause Malfunction Indicator Light (MIL) to glow and remain on until problem is repaired. If light comes on and remains on (light may flash) during vehicle operation, cause of malfunction must be determined using diagnostic (code) charts. See DIAGNOSTIC TROUBLE CODE (DTC) IDENTIFICATION . If a sensor fails, Powertrain Control Module (PCM) will use a substitute value in its calculations to continue engine operation. In this condition, commonly known as limp-in mode, vehicle runs but driveability will not be optimum.

INTERMITTENT FAILURES

Intermittent failures may cause MIL to flicker or glow and go out after intermittent fault goes away. However, corresponding DTC will be retained in PCM memory. If related fault does not reoccur within a certain time frame, related DTC 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 article.

FREEZE-FRAME DATA

According to the 1996 government regulations, engine operating conditions where MIL is illuminated must be recorded. This record, called freeze frame data, is a snap shot of the driving conditions, that is recorded on the PCM freeze frame buffer and is constantly updated with the most current information.

Freeze frame data can only be overwritten with misfire or fuel trim malfunction data. The data can only be erased by clearing associated history DTCs.

RETRIEVING CODES

Note. Codes can be retrieved using a scan tester. Trouble codes are referred to as DTCs.

1. Code retrieval starts with diagnostic circuit check. See «ON-BOARD DIAGNOSTIC II (OBD-II) SYSTEM CHECK»(ref-16268-S13295690262002013100000) . MIL will come on when ignition is on and engine is not running. When engine is started, MIL should go off. If light remains on while engine is running, a DTC is present.
2. If light does not come on with ignition on and engine off, inspect MIL circuit before continuing. If MIL fails to operate, see «ON-BOARD DIAGNOSTIC II (OBD-II) SYSTEM CHECK»(ref-16268-S13295690262002013100000) .
3. To retrieve codes, install scan tool. Select MIL dash lamp control and command the MIL OFF. Ensure MIL light is off and attempt to start engine. If vehicle does not start, go to vehicle NO-START tests. See appropriate BASIC DIAGNOSTIC PROCEDURES article.

CLEARING CODES

1. After repairs are performed, clear PCM memory of all stored codes. Ensure ignition is off. To clear codes, use diagnostic scan tool "clear DTCs" or "clear info" function. Follow instructions supplied by tool manufacturer, when clearing DTCs.
2. DTCs can also be cleared by disconnecting any PCM power source or negative battery cable for at least 30 seconds. However, if disconnecting battery remember that other memory functions (clock, radio, etc.) will need to be reset.

PCM REPROGRAM PROCEDURE

If PCM requires replacement PCM must be reprogrammed using a Tech I or other OBD II compatible scan tool.

SUMMARY

If no hard fault codes are present, driveability symptoms exist or intermittent codes exist, proceed to TESTS W/O CODES article for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.) or intermittent diagnostic procedures.