INTRODUCTION
If no faults were found while performing trouble shooting in the BASIC TESTING article, proceed with ENTERING DIAGNOSTICS-PFI or ENTERING DIAGNOSTICS-TBI . If no fault codes or only pass codes are present, perform trouble shooting procedures the TESTS W/O CODES article for diagnosis by symptom (i.e. ROUGH IDLE, NO START, etc.).
Note. All voltage tests should be performed with a Digital Volt Ohmmeter (DVOM) with a minimum 10-megohm input impedance, unless specifically stated different in testing procedures.
PRETEST INSPECTION-PFI
If PFI system components fail, interruption of fuel supply will result. Engine may be hard to start or not start at all. Unstable idle and/or poor driveability will be noticed. If any of these conditions are present, first perform basic engine checks (ignition, engine adjustments, etc.). See BASIC TESTING article.
If no faults were found while performing basic diagnostic procedures, go to ENTERING DIAGNOSTICS-PFI in this article. If no fault codes or only pass codes are present, go to TESTS W/O CODES article for diagnosis by symptom (i.e. ROUGH IDLE, NO START, etc.).
The self-diagnostic system monitors all input signals from each sensor. If an abnormal input signal occurs, that item is memorized by the ECU and given a code number. See FAULT CHARTS-PFI in this article. Fault codes can be confirmed by using a voltmeter.
If 2 or more systems are non-functional, they are indicated by order of increasing code number. Indication is made by 12-volt pulses of voltmeter pointer. A constant repetition of short 12-volt pulses indicates system is normal. If system is abnormal, voltmeter will pulse between zero and 12 volts.
Note. ECU diagnostic memory is kept by direct power supply from the battery. Memory is not erased by turning off ignition but is erased if battery or ECU is disconnected.
System malfunctions encountered are identified as either hard failures or intermittent failures as determined by the ECU.
Hard Failures
Hard failures cause "malfunction" light to illuminate and remain on until the malfunction 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. If a sensor fails, control unit will use a substitute value in its calculations to continue engine operation. In this condition, vehicle is functional, but loss of good driveability will most likely be encountered.
Intermittent Failures
Intermittent failures may cause "malfunction" light to flicker or illuminate and go out after the intermittent fault goes away. The corresponding trouble code; however, will be retained in control unit memory. If related fault does not reoccur within a certain time frame, related trouble code will be erased from control unit memory. Intermittent failures may be caused by sensor, connector or wiring related problems. See INTERMITTENTS in TESTS W/O CODES article.
Self-Diagnostic Test (Using Voltmeter)
Turn ignition switch to "OFF" position. Connect voltmeter between PFI self-diagnostic output and ground terminals of diagnostic connector, located in glove box or junction box by left side kick panel. (Scheme 8) Turn ignition switch to "ON" position and disclosure of ECU memory will begin.
RETRIEVING CODES-PFI
Note. Oxygen sensor memory is erased when ignition switch is turned to "OFF" position. To diagnose oxygen sensor, drive vehicle a good distance and keep engine running.
Scheme 8
Scheme 9
- Signals will appear on voltmeter as long and short 12-volt pulses. Long pulses represent tens; short pulses represent ones. For example 4 long pulses and 3 short pulses indicates Code 43. Refer to «FAULT CHARTS-PFI»(/mitsubishi/sigma/pre-i-1988-1989/remont/testing-diagnostics/#tests-wcodes) in this article. After recording abnormal code(s), perform necessary repair.
- After repair, turn ignition off and disconnect negative battery cable for 15 seconds to erase ECU memory. Reconnect power supply and repeat self-diagnostics to confirm repair.
CLEARING CODES-PFI
Turn ignition off and disconnect negative battery cable for 15 seconds to erase ECU memory. Reconnect power supply and repeat self-diagnostics to confirm codes are erased.
SUMMARY-PFI
If no hard fault codes (or only pass codes) are present, proceed to TESTS W/O CODES article for diagnosis by symptom (i.e. ROUGH IDLE, NO START, etc.), or intermittent diagnostic procedures.
Scheme 10
Scheme 11
PRETEST INSPECTION-TBI
Before testing TBI components, perform basic engine checks (ignition system malfunctions, incorrect engine adjustments, etc.). See BASIC TESTING article. Perform TBI diagnosis only after conventional components have been inspected.
The diagnostic system, which monitors all input signals from each sensor, is an integral part of the ECU. If an abnormal input signal occurs, that item is memorized by the ECU. There are 6 diagnostic codes which can be confirmed using a voltmeter (Code No. 4 not used in this application). See the DIAGNOSTIC CODES-TBI table.
If 2 or more systems are non-functional, they are indicated in order of increasing code number. Indication is made by deflection of voltmeter pointer. A constant 12 volts indicates system is normal. If system is abnormal, voltmeter will alternate between 0-12 volts every .4 second to display codes. After indication of zero volts for 2 seconds, the next code (if any) will be indicated.
System malfunctions encountered are identified as either hard failures or intermittent failures as determined by the ECU.
Hard failures cause "malfunction" light to illuminate and remain on until the malfunction is repaired. If light comes on and remains on (light may flash) during vehicle operation, cause of malfunction must be determined. If a sensor fails, control unit will use a substitute value in its calculations to continue engine operation. In this condition, vehicle is functional, but loss of good driveability will most likely be encountered.
Intermittent failures may cause "malfunction" light to flicker or illuminate and go out after the intermittent fault goes away. The corresponding trouble code, however, will be retained in control unit memory. If related fault does not reoccur within a certain time frame, related trouble code will be erased from control unit memory. Intermittent failures may be caused by sensor, connector or wiring related problems. See INTERMITTENTS in TESTS W/O CODES article.
Note. ECU abnormal diagnostic memory is kept by direct power from battery. Memory is not erased by turning ignition off, but will be erased if battery or ECU is disconnected. Oxygen sensor memory is erased when ignition is turned off. To diagnose oxygen sensor, drive vehicle a good distance and keep engine running.
Self-Diagnostic Test
Turn ignition switch to "OFF" position. Connect voltmeter to diagnostic connector, located in glove box. (Scheme 8) Proceed to RETRIEVING CODES-TBI.
RETRIEVING CODES-TBI
Turn ignition switch to "ON" position and ECU will display code(s) as pulses on voltmeter. Record any diagnostic codes and perform necessary component repairs. Proceed to CLEARING CODES-TBI .
CLEARING CODES-TBI
After checking and repair, turn ignition off and disconnect negative battery cable for 15 seconds or more to erase ECU code memory.
SUMMARY-TBI
If no hard fault codes (or only pass codes) are present, proceed to TESTS W/O CODES article for diagnosis by symptom (i.e. ROUGH IDLE, NO START, etc.), or intermittent diagnostic procedures.
DIAGNOSTIC CODES-TBI
| Code | Diagnostic Item | Procedure |
|---|---|---|
| 1 | Oxygen Sensor & Computer | (1) O2 Sensor, ECU |
| 2 | Engine Speed Sensor | (1) Ignitor |
| 3 | Airflow Sensor | (1) Airflow Sensor |
| 4 | Not Used | Not Used |
| 5 | Throttle Position Sensor | (1) TPS |
| 6 | ISC Motor Position Sensor | (1) MPS |
| 7 | Coolant Temperature Sensor | (1) CTS |
| (1) Check and repair sensor wiring harness, connectors, and ECU inputs/outputs related to this sensor. | ||
| (1) | Check and repair sensor wiring harness, connectors, and ECU inputs/outputs related to this sensor. |
DIAGNOSTIC CODES-TBI