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Systems Check

  1. Disconnect negative battery cable. Disconnect 10 and 20-pin harness connectors from ECU. Position ECU so inspection lights are easily readable. Reconnect negative battery cable. Start engine and warm up sufficiently. Turn diagnosis start switch on ECU to "OFF" position.
  2. Run engine at 2000 RPM for 5 minutes under no-load. Maintain engine speed at 2000 RPM and verify that Green inspection light goes on and off at least 5 times during 10 seconds. If so proceed to step 5). If light does not respond properly, proceed to next step.
  3. Check exhaust gas sensor harness connector for proper connection. Turn engine off and disconnect negative battery cable. Disconnect 20-pin connector from ECU. Disconnect exhaust gas sensor connector and ground using a jumper wire.
  4. Check for continuity between terminal No. 2 and vehicle body ground. If continuity exists, replace exhaust gas sensor. If continuity does not exist, repair or replace ECU harness and return to step 2).
  5. Turn ignition switch to "OFF" position. Turn diagnosis start switch of ECU to "ON" position. See Fig 1 . Turn ignition switch to "ON" position (do not start). Check status of LED diagnosis lights on ECU. If Red LED is off and Green light is on steady, no problems are present in system.
    Fig 1: Inspection Light & Diagnosis Start Switch Location
    G61615
  6. If Red LED light is on and Green LED light is flashing with long pauses between flashes, turn ignition switch to "OFF" position. See Fig 1 . Verify that each harness connector is connected securely. If so, go to step 7). If not, correct condition and return to step 5). If Red LED light is on and Green LED light stays on longer than short pauses between flashes, go to step 12).
  7. Disconnect each harness connector. Measure resistance between harness connector and 20-pin connector of ECU. Measure resistance of coolant temperature sensor and air temperature sensor at varying degrees of heat. See TEMPERATURE SENSING COMPONENT RESISTANCES  .
    TEMPERATURE SENSING COMPONENT RESISTANCES

    Sensor Between Terminals (1) Temp. Degrees °F(°C) Ohms
    Coolant 8 & 19 Above 68 (20) (2)
    Coolant 8 & 19 Below 68 (20) (3)
    Air 1 & 19 Above 68 (20) (2)
    Air 1 & 19 Below 68 (20) (3)
    (1) Terminal No. 19 is ground (-).
    (2) 2900 ohms or less.
    (3) 2100 ohms or more.
  8. If resistances are as specified, correct or replace ECC wiring harness. If resistance is not as specified, replace malfunctioning sensor. Measure voltage of vacuum sensor (step 9). On Federal vehicles check the operation of the barometric pressure sensor.
  9. To check vacuum sensor, disconnect 20-pin connector (if disconnected). Disconnect each harness connector. Disconnect vacuum hose from vacuum sensor and connect a hand vacuum pump to sensor. Install a voltmeter between terminals No. 9 (+) and ground of vacuum sensor. With no vacuum applied, voltmeter should read 4 volts. With 26 in. Hg applied, voltmeter should read .5 volts.
  10. If voltage measurements are as specified, replace control unit and return to step 5). If voltage readings are not as specified, turn ignition switch to "OFF" position and disconnect each sensor harness connector. Connect vacuum sensor to battery using jumper wires. Install voltmeter and measure voltage. See Fig 2 .
    Fig 2: Vacuum Sensor Test Connections
    G61616
  11. With no vacuum applied to sensor voltmeter should read 4 volts. With vacuum hose from vacuum sensor disconnected and a hand vacuum pump connected to sensor, apply 26 in. Hg to vacuum sensor. Voltage should read .5 volts. If voltage is as specified, proceed to next step. If voltage is not as specified, replace vacuum sensor and return to step 5).
  12. If Red LED light is on and Green LED light is flashing on longer than pauses between flashes, measure the resistance value of each of the listed solenoid valves and relays. See SOLENOID & RELAY RESISTANCES  table.
    SOLENOID & RELAY RESISTANCES

    Application Check Terminal
    Air-Fuel Ratio Solenoid 30-50
    Air Injection Solenoid 25-45
    EGR & Canister Purge Solenoid 25-45
    Fuel Cut-Off Solenoid 25-45
    Mixture Heater Relay 60-85
    Richer Solenoid (Federal Models Only) 20-40
    Vacuum Control Modulator (Federal Models Only) 25-45
  13. If vacuum control modulator, solenoid valves or relay resistance are out of specification, replace component(s) and return to step 5). If all component resistances are within specifications, reconnect harness connectors. Turn ignition switch to "ON" position.
  14. Measure voltage between each terminal of connectors and ground. See SOLENOID VOLTAGES  table. If voltage readings are within specifications, replace control unit and return to step 5). If voltages are not within specifications repair or replace appropriate wiring harness. When checking voltages, connect voltmeter between terminal listed in the SOLENOID VOLTAGES  table and body ground.
SOLENOID VOLTAGES

Solenoid Terminal Voltage
Air-Fuel Ratio Solenoid F 12-14
Air Injection Solenoid H 12-14
EGR & Canister Purge Solenoid C 12-14
Fuel Cut-Off Solenoid G 12-14
Mixture Heater Relay 3 12-14
Richer Solenoid (Federal Models Only). B 12-14
Vacuum Control Modulator (Federal Models Only) I 12-14
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