Engine Controls - Tests W/codes Porsche 911 Carrera 993

INTRODUCTION

If no faults were found while performing the basic checks in the BASIC TESTING article, proceed with the self-diagnostic tests in this article. Also, see the SYSTEM/COMPONENT TESTS article.

SELF-DIAGNOSTIC SYSTEM

Digital Motor Electronics (DME) control unit can store fault codes related to fuel injection, ignition, and (engine) knock regulating systems. Detected faults are stored for at least 50 engine starts. If positive battery cable or DME control unit is disconnected, fault code memory and system adaptation will be cleared.

MALFUNCTION INDICATOR LIGHT (MIL)

All models are equipped with a MIL (or CHECK ENGINE light). Light comes on if component related to fuel injection and/or ignition system fails. MIL is installed in oil temperature/pressure gauge cluster. Light comes on as a self-test when ignition switch is in ON position.

After engine starts, throttle valve closes and MIL goes out to indicate no codes are present. If MIL remains on, a fault is present (hard failure) in DME engine management system. If MIL comes on (flickers) while vehicle is driven, a fault in DME engine management system has been identified (intermittent failure).

If idle speed switch is open during starting, MIL will come on. As soon as idle speed switch closes while vehicle is driven, MIL goes out after a 4-second delay.

If full throttle switch is faulty (shorted to ground), MIL will remain on constantly. Some fault codes cannot be displayed using MIL. In such cases, retrieve fault codes through diagnostic connector, and repair conditions causing MIL to come on. See USING DIAGNOSTIC CONNECTOR under RETRIEVING CODES. (Scheme 1)or (Scheme 2).

Scheme 1

Scheme 2

Using Malfunction Indicator Light (MIL)

1. Turn ignition on. Ensure MIL comes on. Depress and hold accelerator pedal at Wide Open Throttle (WOT) for 3-5 seconds.
2. After MIL goes out and comes on again, release accelerator pedal. This on-off period indicates self-diagnostic system is preparing to output diagnostic codes. (Scheme 3)
3. Next MIL 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.
4. Continue to depress and release accelerator pedal until Code 1000 is displayed, indicating end of output. (Scheme 3)

Using Diagnostic Connector

1. Ensure transmission is in Park or Neutral and ignition is off. Connect Porsche System Tester (9288) or Porsche Flashing Code Tester (9268) and Adapter (9268/2) to Diagnostic Link Connector (DLC). (Scheme 1)or (Scheme 2).
2. If using system tester, turn tester on and follow instructions displayed. In addition to reading fault memory, tester can activate a number of components.
3. If using flashing code tester and adapter, 4-digit fault codes will be flashed by tester. If number 1 is displayed in second digit of code, fault was present during last vehicle operation. If number 2 is displayed in second digit, fault was not present when vehicle was last operated. See «FAULT CODE IDENTIFICATION»(/porsche/911-carrera/993-1993-1998/remont/testing-diagnostics/#engine-controls-tests-wcodes).

Scheme 3

READING INPUT & OUTPUT SIGNALS

Some input and output signals can be checked using either code tester. To check input signals, operate accelerator pedal and A/C switch as described and check for LED to flash indicating correct operation. Refer to the appropriate OUTPUT SIGNALS CODE IDENTIFICATION or INPUT SIGNALS CODE IDENTIFICATION .

OUTPUT SIGNALS CODE IDENTIFICATION

INPUT SIGNALS CODE IDENTIFICATION

FAULT CODE IDENTIFICATION

Using Malfunction Indicator (CHECK ENGINE) Light

Ensure fault causing MIL to come on has been repaired. Depress and hold accelerator pedal at WOT for more than 12 seconds. Ensure MIL goes out briefly after 3, 7 and 10-second intervals, indicating fault code memory has been cleared.

Disconnecting DME Control Unit Connector

To clear codes stored in memory, momentarily disconnect electrical connector from DME control unit. 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.

CODE 1111: DME POWER SUPPLY

1. Battery Voltage (Keep-Alive Memory) Circuit Disconnect DME control unit. Connect Digital Volt-Ohmmeter (DVOM) between terminal No. 24 (ground) and terminal No. 18 (battery voltage). (Scheme 4) DVOM should indicate battery voltage. If battery voltage is not present, check Red wire back to fuse block and battery, or check Brown ground wire.
2. Ignition Voltage (DME Relay) Circuit Connect DVOM between terminal No. 24 (ground) and terminal No. 37 (ignition voltage). (Scheme 4) Turn ignition on. DVOM should ind icate battery voltage. If battery voltage is not present, check Gray/Brown wire back to DME relay or Brown ground wire.

CODE 1112: IDLE SPEED SWITCH SHORT CIRCUIT TO GROUND

1. Disconnect DME control unit. Connect DVOM between terminal No. 24 (ground) and terminal No. 52 (idle speed switch). (Scheme 4) With throttle valve closed, resistance should be less than 10 o hms.
2. Open throttle valve beyond one-degree opening angle. With throttle valve open, ohmmeter reading should be infinite. If readings are incorrect, measure resistance directly at idle speed switch and adjust if necessary. See the «ADJUSTMENTS»(/porsche/911-carrera/993-1993-1998/remont/adjustments/#engine-controls-adjustments) article.

Scheme 4

CODE 1113: FULL THROTTLE SWITCH SHORT CIRCUIT TO GROUND

1. Disconnect DME control unit. Connect a DVOM between terminal No. 24 (ground) and terminal No. 53 (full throttle switch). (Scheme 4) With throttle valve closed, ohmmeter reading should be infinite.
2. With throttle valve at least 2/3 open, reading should be less than 10 ohms. If readings are incorrect, measure resistance directly at full throttle switch and adjust if necessary. Refer to the «ADJUSTMENTS»(/porsche/911-carrera/993-1993-1998/remont/adjustments/#engine-controls-adjustments) article.

CODE 1114: ENGINE COOLANT TEMPERATURE SENSOR

Disconnect the DME control unit. Connect a DVOM between terminal No. 30 (ground) and terminal No. 45 (engine temperature sensor). Refer to the ENGINE COOLANT TEMPERATURE SENSOR RESISTANCE. (Scheme 4) If read ings are incorrect, check resistances directly on sensor.

ENGINE COOLANT TEMPERATURE SENSOR RESISTANCE

CODE 1115: IDLE SPEED SWITCH OPEN CIRCUIT

Test procedure for Code 1115 is the same as that for Code 1112. Cause may be an incorrectly set throttle valve switch or accelerator cable.

CODE 1121: MAF SENSOR

1. Voltage Supply - Connect DVOM between ground and terminal No. 3 of MAF sensor wiring harness connector. (Scheme 5) Turn ignition on to check voltage supply to sensor. If reading is 4.7-5.3 volts, go to next step. If voltage is not 4.7-5.3 volts, check Blue/Green wire back to DME control unit.
2. Voltage Drop - Disconnect air filter hose. Using jumper wires, connect terminal No. 3 of MAF sensor wiring harness connector to terminal No. 3 of sensor, and connect terminal No. 4 of wiring harness connector to terminal No. 4 of sensor.
3. Connect DVOM between ground and MAF sensor terminal No. 2. Turn ignition on to check voltage drop across sensor. With MAF sensor plate closed, reading should be 250-260 millivolts.
4. Using screwdriver handle, press MAF sensor plate to full throttle position. Reading should gradually increase to about 4.6 volts. If voltage values are incorrect, replace MAF sensor.

Scheme 5

Voltage Supply

Disconnect idle speed positioner. (Scheme 4) Connect DVOM between ground and terminal No. 2 of idle speed positioner wiring harness connector. Turn ignition on to check voltage supply to positioner. If battery voltage is not present, check Blue wire back to DME control unit. If battery voltage is present, go to CONTROL SIGNAL TEST.

Control Signal Test

Using DME System Tester (9288) in ACTUAL VALUE menu, check idle speed control duty cycle. If tester is not available, idle speed control circuit may also be tested using an oscilloscope and DME Test Lead (Bosch No. 1-684-463-093). A square-wave pattern of approximately 100 Hertz (Hz.) frequency must be present when engine is running.

CODE 1123: OXYGEN REGULATION STOP

Fault code is set if oxygen regulation is unable to operate within control range. Fuel mixture may be too lean because of additional air entering intake system. A too rich condition may be caused by a sticking (open) fuel injector.

Check the idle speed and mixture (CO level). Refer to the ADJUSTMENTS article. If fuel mixture is too lean, check intake system for leaks. If fuel mixture is too rich, check fuel pressure. Refer to the BASIC TESTING article. If fuel pressure is okay, replace leaking fuel injector(s).

CODE 1124: HEATED OXYGEN SENSOR

1. Disconnect oxygen sensor. Start engine and warm it to normal operating temperature. Connect DVOM between ground and oxygen sensor voltage signal wire. (Scheme 4)
2. Note voltage on DVOM. Accelerate engine to enrich mixture and note voltage reading on DVOM. DVOM must indicate a change in voltage signal. Reading will vary between 150-900 millivolts depending on air/fuel mixture.

Note. If DME control unit detects an oxygen sensor voltage signal of more than one volt or less than 0.1 volt, the control unit will switch over to open loop operation.

CODE 1125: INTAKE AIR TEMPERATURE SENSOR

Disconnect DME control unit. Connect DVOM between terminal No. 26 (MAF meter ground) and terminal No. 44 (intake air temperature sensor). See the INTAKE AIR TEMPERATURE SENSOR RESISTANCE. (Scheme 4) If readings are incorrect, check resistances directly on sensor by connecting ohmmeter between MAF sensor terminals No. 1 and 4. (Scheme 5)

INTAKE AIR TEMPERATURE SENSOR RESISTANCE

CODE 1131: KNOCK SENSOR NO. 1

Check knock sensor and bracket for proper installation. Check sensor connectors for loose, corroded or damaged terminals. Check knock sensor circuits/wiring harness (Brown and White wires back to DME control unit). If necessary, replace knock sensor.

Note. If knock sensor is faulty, ignition timing will be retarded 6 degrees on crankshaft.

CODE 1132: KNOCK SENSOR NO. 2

Test procedure for Code 1132 is the same as that for Code 1131.

CODE 1133: DME CONTROL UNIT (KNOCK CONTROL)

If knock control portion of DME control unit is faulty, ignition timing will be retarded 6 degrees. Replace DME control unit.

CODE 1134: HALL EFFECT SENSOR

Check Hall Effect sensor, in distributor, for proper installation. Check sensor connectors for loose, corroded or damaged terminals. Hall Effect sensor terminal No. 3-to-terminal No. 31 circuit at DME control unit is the voltage supply circuit, terminal No. 1-to-terminal No. 30 circuit at DME is the ground circuit, and terminal No. 2-to-terminal No. 8 circuit at DME is the signal return circuit. Replace sensor if voltage supply, ground, and signal return circuits are okay.

CODE 1141: DME CONTROL UNIT

Replace faulty DME control unit.

CODE 1143: FUEL TANK VENTING SOLENOID

1. Activation Test - Using DME System Tester (9288) in DRIVE LINK ACTIVATION menu, actuate fuel tank venting valve (solenoid) connector. Check voltage signal at fuel tank venting valve terminal No. 1. (Scheme 4) If voltage signal is not present, check Yellow/Green wire back to DME control unit.
2. Control Signal Test - Fuel tank venting solenoid circuit may also be tested using an oscilloscope and DME Test Lead (Bosch No. 1-684-463-093). Control signal test must be performed within 7 minutes after starting engine, at operating temperature.
3. A square-wave pattern, with an initial voltage spike, must be present when engine is running. Square-wave signal becomes wider as airflow increases. If signal is not present, check wiring harness and connectors. If necessary, replace DME control unit.

CODE 1144: RESONANCE PLATE

Each time ignition is turned on, a ground pulse is supplied by DME control unit to resonance plate solenoid. If vacuum is present, plate is audibly opened and closed.

Using an oscilloscope and DME System Tester (9288) in the DRIVE LINK ACTIVATION menu, actuate resonance plate. A signal must be visible on oscilloscope when ignition is turned on or when actuating plate. If signal is not present, check Green/White wire back to DME control unit. Replace DME control unit if resonance plate moves freely, and vacuum and ground pulse signal are present.

CODE 1145: MALFUNCTION INDICATOR LIGHT (MIL)

A ground path for Malfunction Indicator Light is provided by DME control unit over terminal No. 22 (Green/Gray wire). Ensure MIL bulb filament is not burned out. Check malfunction indicator light circuit by turning ignition off.

Disconnect DME control unit, and ground terminal No. 22 (Green/Gray wire). With ignition on, MIL should come on. If light does not come on, check wiring harness and connectors. If necessary, replace DME control unit.

Note. Green/Gray wire is also routed to diagnostic connector. Ensure wire leading to diagnostic connector is not shorted to battery voltage or ground.

CODES 1151 THROUGH 1156: FUEL INJECTORS

1. Disconnect fuel injector(s). Connect DVOM between ground and terminal No. 2 of fuel injector connector. (Scheme 4) Turn ignition on, and check voltage supply to fuel injector. If battery voltage is not present, check Red/White wire back to fuse/relay block.
2. If battery voltage is present, use DVOM to measure resistance across injector terminals. If resistance is not 16 ohms, replace injector. Repeat test for each injector.

ECM LOCATION

DME control unit is located under driver's seat.

SUMMARY

If no hard codes or only pass codes exist, if driveability symptoms or intermittent codes exist, refer to the BASIC TESTING or the SYSTEM/COMPONENT TESTS articles.

Poses Online

See also:
• BASIC TESTING
• SYSTEM/COMPONENT TESTS
• ADJUSTMENTS
• USING DIAGNOSTIC CONNECTOR
• FAULT CODE IDENTIFICATION
• 1111
• 1112
• 1113
• 1114
• 1115
• 1121
• 1123
• 1124
• 1125
• 1131
• 1132
• 1133
• 1134
• 1141
• 1143
• 1144
• 1145
• 1151
• CONTROL SIGNAL TEST