GM Metro/Sprint 1985-1993 Repair Guide

Diagnostic Trouble Codes-EFI Turbo System

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READING CODES



See Figure 1

Once the integrity of the system is confirmed, enter the Diagnostic Mode and read any stored codes. Once the Diagnostic Mode is engaged, the dash warning lamp should begin to flash.

The Sprint uses a Code 12 to indicate that no other codes are stored. If a fault is in memory, it will be broadcast as soon as the system enters Diagnostic Mode. The codes are stored and transmitted in numeric order from lowest to highest; each fault code is transmitted 3 times before moving to the next.

The order of codes in the memory does not indicate the order of occurrence.

Record each code transmitted for later reference. Once all codes have been sent, the memory may need to be cleared during diagnostics. If there are no codes stored, but a driveability or emissions problem is evident, inspection of individual components is necessary.

To retrieve codes from the ECM:

  1. When the ignition switch is turned ON with the engine not running the CHECK ENGINE light illuminates. This indicates the circuit of the CHECK ENGINE light is functioning properly.
  2.  
  3. If the EFI system is functioning properly, the CHECK ENGINE light should go out when the engine is started.
  4.  
  5. If a malfunction exists in the signal to the ECM when the engine is running, the CHECK ENGINE light remains illuminated as long as the malfunction exists.
  6.  
  7. If a malfunction in the input signal to the ECM is detected even once, it will be kept in the ECM memory in the form of a diagnostic code.
  8.  
  9. The memorized code will be stored until the power from the battery to the ECM is disconnected. Therefore, after correcting the problem area, erase the ECM memory by disconnecting the negative battery cable for 20 seconds or longer.
  10.  
  11. When the diagnosis switch, located under the left side of the instrument panel, to the right of the steering column, is turned ON , the CHECK ENGINE light flashes to indicate the diagnostic code in the ECM memory.
  12.  
  13. When the ECM is damaged, the CHECK ENGINE light will remain ON instead of flashing codes.
  14.  
  15. The CHECK ENGINE light flashing pattern of each diagnostic code represents a 2-digit number. The diagnostic code repeats until the switch is turned OFF .
  16.  
  17. If two or more areas are involved the CHECK ENGINE light indicates each code corresponding to the area of trouble three times and in the increasing order of the code numbers. After all codes are displayed, the sequence is repeated.
  18.  



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Fig. Fig. 1: 1987-88 EFI turbo diagnostic codes

CIRCUIT/COMPONENT DIAGNOSIS AND REPAIR



Using the appropriate chart(s) based on the Diagnostic Circuit Check, the fault codes and scan tool data will lead to diagnosis and checking of a particular circuit or component. It is important to note that the fault code indicates a fault or loss of signal in an ECM-controlled system, not necessarily in the specific component. Detailed procedures to isolate the problem are included in each code chart; these procedures must be followed accurately to insure timely and correct repair. Following the procedure will also insure that only truly faulty components are replaced.

CLEARING CODES



Stored fault codes may be erased from memory at any time by removing power from the ECM for at least 30 seconds. This time period must be increased as the temperature drops. It may be necessary to clear stored codes during diagnosis to check for any recurrence during a test drive, but the stored codes must be written down when retrieved. The codes may still be required for subsequent troubleshooting. Whenever a repair is complete, the stored codes must be erased and the vehicle test driven to confirm correct operation and repair.

The ignition switch must be OFF any time power is disconnected or restored to the ECM. Severe damage may result if this precaution is not observed.

Removing the TAIL LAMP fuse from the under dash fuse box will interrupt power to the ECM without blanking other memories within the vehicle. The pink, 30 amp main fuse may be removed from the underhood fuse holder on the right front fender apron, but this will also disconnect power to the clock and the radio.

COMPONENT TESTING



Electronic Control Module (ECM)

See Figure 2

The ECM is grounded to the surge tank. A loose ground may hinder proper operation of the ECM. Check to make sure that it is properly and securely grounded. The ECM is located under the left side of the dash to the left of the steering column.

  1. Turn the ignition switch OFF .
  2.  



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Fig. Fig. 2: Checking the ECM for proper ground

  1. Disconnect the left coupler from the ECM by pushing the lockdown.
  2.  
  3. Check for continuity between each terminal of the Black/Green lead wire and Black/Blue lead wire and ground with an ohmmeter.
  4.  
  5. After checking, connect the coupler to the ECM securely.
  6.  

Airflow Meter

See Figure 3

  1. Turn the ignition switch OFF .
  2.  



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Fig. Fig. 3: Checking airflow meter resistance

  1. Disconnect the airflow meter connector.
  2.  
  3. Check for resistance between the terminals of the airflow meter with an ohmmeter as described in the illustration.
  4.  

Oxygen Sensor
  1. Warm the engine to normal operating temperature.
  2.  
  3. Disconnect the connector of the oxygen sensor.
  4.  
  5. Connect a voltmeter between the sensor side terminal and ground.
  6.  

Never apply voltage to the oxygen sensor as it may cause damage to the sensor.

  1. With the engine running at 3000 rpm, check that the voltage from oxygen sensor exceeds 0.7 volts.
  2.  
  3. With the engine idling, check that the voltage from oxygen sensor is zero volts.
  4.  
  5. After checking, reconnect oxygen sensor connector.
  6.  

Coolant Temperature Sensor

See Figure 4



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Fig. Fig. 4: Coolant temperature sensor resistance

  1. Disconnect electrical connector from coolant temperature sensor.
  2.  
  3. Using an ohmmeter, check resistance between the sensor terminals.
  4.  
  5. With engine cold, resistance should be approximately 2000 ohms.
  6.  
  7. With engine at normal operating temperature, resistance should be less than 500 ohms.
  8.  

Starter Injector Time Switch
  1. Disconnect electrical connector from coolant temperature sensor.
  2.  
  3. Using an ohmmeter, check resistance between the sensor terminals.
  4.  
  5. With coolant temperature lower than 66°F (19°C), resistance should be 34-39 ohms.
  6.  
  7. With coolant temperature higher than 77°F (25°C), resistance should be 68-78 ohms.
  8.  

Main Relay

See Figures 5, 6 and 7

The main relay and fuel pump relay sit side by side on a bracket at the shock tower. The main relay has Black, Black/White, White/Blue and White/Green lead wires.

  1. Check that main relay makes a sound when the ignition switch is turned ON .
  2.  
  3. With ignition switch ON , check for battery voltage between the top and bottom two terminals.
  4.  
  5. Check that there is continuity between terminals 3 and 4 when the battery is connected to terminals 1 and 2.
  6.  



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Fig. Fig. 5: Checking main relay voltage



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Fig. Fig. 6: Checking main relay resistance



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Fig. Fig. 7: Checking main relay operation

Ignition Signal

See Figure 8

This inspection should only be performed when the vehicle fails to start.



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Fig. Fig. 8: Checking ignition signal voltage

  1. With the ignition switch OFF , disconnect the right connector from the ECM.
  2.  
  3. Check for battery voltage at the White lead wire when the ignition switch is ON .
  4.  
  5. If battery voltage is not detected, check ignition coil and circuit.
  6.  
  7. Connect ECM coupler after ensuring that ignition switch is OFF .
  8.  

Engine Start Signal

See Figure 9



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Fig. Fig. 9: Checking engine start signal voltage

  1. With ignition OFF , remove the left coupler from the ECM.
  2.  
  3. Check for battery voltage at the Black/Yellow wire when the starter motor is turning.
  4.  
  5. If battery voltage is not detected, check starter motor and circuit.
  6.  
  7. Connect ECM coupler after ensuring that ignition switch is OFF .
  8.  

Fuel Cut Check
  1. Warm the engine to normal operating temperature.
  2.  
  3. While listening to the sound of the injectors using a mechanics scope, increase engine speed to 3000 rpm.
  4.  
  5. Check to make sure that sound of injectors stops when throttle is closed suddenly and is not heard again when engine speed is increased to less than 1900 rpm.
  6.  
  7. If injector operation sound does not disappear, check throttle position sensor.
  8.  

 
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