INTRODUCTION
If no faults were found while performing BASIC TESTING , proceed with self-diagnostics. Also see SYSTEM/COMPONENT TESTS article in this section.
Note. Only limited information on the self-diagnostic system is available from manufacturer.
SELF-DIAGNOSTIC SYSTEM
The Digital Motor Electronics (DME) control unit has the ability to store fault codes related to fuel injection and ignition systems. Detected faults are stored for at least 50 engine starts. If positive battery cable or DME control unit connector is disconnected, fault code memory and system adaptation will be cleared.
Hard Failures
Hard failures cause CHECK ENGINE light to illuminate 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. If a sensor fails, the control unit 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 CHECK ENGINE light to flicker or illuminate. Light goes out after intermittent fault goes away. However, the corresponding trouble code will be stored in ECU memory. If fault does not reoccur within a certain time frame, related code will be erased from ECU memory. Intermittent failures may be caused by sensor, connector or wiring related problems. See INTERMITTENTS in TESTS W/O CODES article in the ENGINE PERFORMANCE Section.
CHECK ENGINE LIGHT
All 1991 models are equipped with a CHECK ENGINE light. Light comes on if component related to fuel injection and/or ignition system fails. The CHECK ENGINE light is installed in oil temperature/pressure gauge cluster. Light comes on as a self-test when ignition switch is in ON position.
After the engine starts, the throttle valve closes, and the CHECK ENGINE light goes out to indicate that no codes are present. If the CHECK ENGINE light remains on, a fault is present (hard failure) in the DME engine management system. If the CHECK ENGINE light comes on (flickers) while driving, a fault in the DME engine management system has been identified (intermittent failure).
If the idle speed switch is open during the starting sequence, the CHECK ENGINE light will come on. As soon as the idle speed switch closes while driving, the CHECK ENGINE light goes out after a 4-second delay.
If full throttle switch is faulty (shorted to ground), the CHECK ENGINE light will remain on constantly. Some fault codes CANNOT be displayed using the CHECK ENGINE light. In such cases, retrieve the fault code(s) through diagnostic connector, and repair condition(s) causing the CHECK ENGINE light to come on. See USING DIAGNOSTIC CONNECTOR under RETRIEVING CODES.
Using CHECK ENGINE Light
- Turn ignition switch on. Depress and hold accelerator pedal at Wide Open Throttle (WOT) for 3-5 seconds. After CHECK ENGINE light goes out and comes on again, release accelerator pedal. This on-off period indicates that self-diagnostic system is preparing to output diagnostic codes. (Scheme 1)
- The next CHECK ENGINE light on-off periods will represent first fault code stored. Record fault code and again depress and hold accelerator pedal at WOT for 3-5 seconds. Release accelerator pedal and record second fault code stored.
- Continue to depress and release accelerator pedal until Code 1000 is displayed, indicating end of output. (Scheme 1)
Scheme 1
Using Diagnostic Connector
- Ensure transmission is in Park or Neutral, and ignition is off. Diagnostic connector is located underneath a cover, in front passenger's footwell. Connect Porsche System Tester (9288), or Porsche Flashing Code Tester (9268) with Adapter Lead (9268/2) to diagnostic connector.
- If system tester is used, turn tester on and follow instructions displayed. In addition to reading fault memory, it is possible to activate a number of components with this tester.
- If flashing code tester and adapter lead is used, the 4-digit fault code(s) will be flashed by the tester. If the number 1 is displayed in the second digit of the code, then fault was present during the last vehicle operation. If the number 2 is displayed in the second digit, then fault was not present when vehicle was last operated. See «FAULT CODE IDENTIFICATION»(/porsche/911-turbo/964-1988-1994/remont/testing-diagnostics/#engine-controls-tests-wcodes) .
| Code (1) | System Affected | Probable Cause |
|---|---|---|
| 1000 (2) | End Of Output | |
| 1111 | DME Power Supply | Power Supply Less Than 10 Volts Or Greater Than 16 Volts |
| 1112 (2) | Idle Speed Switch | Short In Ground Circuit |
| 1113 | Full Throttle Switch | Short In Ground Circuit |
| 1114 (2) | Engine Temperature Sensor | Open Circuit |
| 1121 (2) | Airflow Sensor | (3) Signal Not Plausible |
| 1123 (2) | Oxygen Sensor | Air/Fuel Mixture Too Rich/Too Lean |
| 1124 (2) | Oxygen Sensor | Open/Shorted Ckt Or Faulty Sensor |
| 1125 | Intake Air Temp. Sensor | Open/Short Circuit |
| 1131 | Knock Sensor No. 1 | (3) Signal Not Plausible |
| 1132 | Knock Sensor No. 2 | (3) Signal Not Plausible |
| 1133 | Knock Regulation | Knock Computer Faulty |
| 1134 | Hall Effect Sensor | Open/Short Circuit |
| 1141 (2) | DME Control Unit | DME Control Unit Faulty |
| 1151 (2) | Fuel Injector No. 1 | Open/Short Circuit |
| 1152 (2) | Fuel Injector No. 2 | Open/Short Circuit |
| 1153 (2) | Fuel Injector No. 3 | Open/Short Circuit |
| 1154 (2) | Fuel Injector No. 4 | Open/Short Circuit |
| 1155 (2) | Fuel Injector No. 5 | Open/Short Circuit |
| 1156 (2) | Fuel Injector No. 6 | Open/Short Circuit |
| 1500 (2) | System Okay | No Faults Stored In Memory |
| (1) Except for Code 1000 and Code 1500, the second digit of all other codes can also be a 2, indicating that fault did not exist during last operation of vehicle. (2) On 1991 models, these codes can also be displayed by CHECK ENGINE light. Other flashing codes are also possible but DO NOT represent a warning regarding CHECK ENGINE light. (3) Signal of a monitored component is not conforming with memory contents of DME control unit. The control unit recognizes that there is a faulty signal, but cannot always recognize the cause of the faulty signal. | ||
| (1) | Except for Code 1000 and Code 1500, the second digit of all other codes can also be a 2, indicating that fault did not exist during last operation of vehicle. |
| (2) | On 1991 models, these codes can also be displayed by CHECK ENGINE light. Other flashing codes are also possible but DO NOT represent a warning regarding CHECK ENGINE light. |
| (3) | Signal of a monitored component is not conforming with memory contents of DME control unit. The control unit recognizes that there is a faulty signal, but cannot always recognize the cause of the faulty signal. |
FAULT CODE IDENTIFICATION
READING INPUT & OUTPUT SIGNALS
Some input and output signals can be checked with both testers. See INPUT SIGNALS CODE IDENTIFICATION and OUTPUT SIGNALS CODE IDENTIFICATION tables under INPUT & OUTPUT SIGNAL IDENTIFICATION .
INPUT & OUTPUT SIGNAL IDENTIFICATION
| Code | Input Signals | (1) Action |
|---|---|---|
| 1000 | End Of Output | None |
| 1332 | 10-Idle Speed Switch | Operate Accelerator Pedal Lightly |
| 1333 | 11-Full Throttle Switch | Operate Accelerator To WOT |
| 1334 | (2) 12-A/C Activation | Switch On Air Conditioning |
| 1335 | (3) 13-A/C Activation | Switch Off Air Conditioning |
| (1) After action is taken, LED should go out and 0000 should be displayed on tester after about 3 seconds. (2) Input occurs at terminal No. 41 of DME control unit. (3) Input occurs at terminal No. 40 of DME control unit. | ||
| (1) | After action is taken, LED should go out and 0000 should be displayed on tester after about 3 seconds. |
| (2) | Input occurs at terminal No. 41 of DME control unit. |
| (3) | Input occurs at terminal No. 40 of DME control unit. |
INPUT SIGNALS CODE IDENTIFICATION
| Code (1) | Output Signals |
|---|---|
| 1311 | 1-Fuel Injector No. 1 |
| 1312 | 2-Fuel Injector No. 2 |
| 1313 | 3-Fuel Injector No. 3 |
| 1314 | 4-Fuel Injector No. 4 |
| 1315 | 5-Fuel Injector No. 5 |
| 1316 | 6-Fuel Injector No. 6 |
| 1321 | 7-Idle Speed Control |
| 1322 | 8-Fuel Tank Vent Solenoid |
| 1323 | 9-Resonance Flaps |
| (1) Activation of component may cause difficult engine starting afterward. | |
| (1) | Activation of component may cause difficult engine starting afterward. |
OUTPUT SIGNALS CODE IDENTIFICATION
Make sure the fault causing the CHECK ENGINE light to come on has been repaired, then depress and hold accelerator pedal at WOT for more than 12 seconds. The CHECK ENGINE light goes out briefly after 3, 7 and 10-second intervals to indicate that fault code memory has been cleared.
Disconnecting DME Control Unit Connector
To clear codes stored in memory, momentarily disconnect the electrical connector from DME control unit. The fault code memory and system adaptation will be cleared.
Note. Fault code memory may also be cleared using Porsche system tester or Porsche flashing code tester.
DME CONTROL UNIT LOCATION
The DME control unit is located under the driver's seat.
SUMMARY
If no hard fault codes (or only pass codes) are present, driveability symptoms exist or intermittent codes exist, proceed to the BASIC TESTING article in this section or go to the appropriate SYSTEM/COMPONENT TESTS article in this section.
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