Diagnostic Aids

Perform this test only when directed by QUICK TEST . This test is intended to diagnose the following:

• Wiring harness circuits (CHT and SIG RTN).
• Faulty CHT sensor.
• Faulty Powertrain Control Module (PCM).

Fig 1: CHT Test Circuits & Connector Terminals

1. 1) DTC P1288:  DTC P1228 indicates CHT sensor is out of self-test range (1.2-3.7 volts). Possible causes for this fault are:
   • Engine overheating.
   • Low coolant level.
   • Faulty sensor.
   • Faulty sensor connector.
   • Poor thermostat operation.

   Start engine and raise speed to 2000 RPM. Ensure upper radiator hose is warm and pressurized. Perform KOER SELF-TEST . Check for DTC P1288. If DTC P1288 is not present, service code and repeat QUICK TEST . If DTC P1288 is present, go to next step.

2. 2) Check VREF Circuit Voltage  Turn ignition off. Disconnect TP sensor. Measure voltage between VREF and SIG RTN terminals at TP sensor wiring harness connector. If voltage is 4-6 volts, go to next step. If voltage is not 4-6 volts, reconnect sensor and go to CIRCUIT TEST C.
3. 3) Check CHT Sensor Circuit Resistance  Turn ignition off. Disconnect CHT sensor. Measure resistance between CHT sensor terminals. See CHT SENSOR SPECIFICATIONS  table. If resistance is within specification, go to next step. If resistance is not within specification, replace sensor and repeat QUICK TEST .
4. 4)  Leave CHT sensor disconnected. Start engine and raise speed to 2000 RPM. Measure resistance between CHT sensor terminals. See CHT SENSOR SPECIFICATIONS  table. If resistance is within specification, replace PCM and repeat QUICK TEST . If resistance is not within specification, replace sensor and repeat QUICK TEST .
   NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 4) to step 10). No test procedures have been omitted.
5. 10) DTC P1289  This code indicates CHP sensor signal is greater than self-test maximum. Possible causes for this fault are:
   • Open circuit.
   • Faulty CHT sensor.
   • Faulty PCM.

   Turn ignition off. Disconnect CHT sensor wiring harness connector. Inspect for damage and repair as necessary. Connect jumper wire between sensor terminals. Connect scan tester to DLC. Access CHT PID on scan tester. Turn ignition on. If PID voltage is less than 0.2 volts, replace CHT sensor and repeat QUICK TEST . If PID voltage is 0.2 volts or more, remove jumper wire and go to next step. If scan tester is unable to access TP PID, go to next step.

6. 11) Check TP Circuit Continuity  Turn ignition off. Leave TP sensor disconnected. Disconnect PCM 104-pin connector. Inspect connector for damage and repair as necessary. Install EEC-V Breakout Box (014-00950), leaving PCM disconnected. Measure resistance between test pin No. 66 (CHT) and CHT terminal of CHT sensor wiring harness connector. Measure resistance between test pin No. 91 (SIG RTN) and SIG RTN terminal of CHT sensor wiring harness connector. If either resistance measurement is less than 5 ohms, replace PCM and repeat QUICK TEST . If both resistance measurements 5 ohms or more, repair open circuit, repeat QUICK TEST .
   NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 11) to step 20). No test procedures have been omitted.
7. 20) DTC P1290  This code indicates CHP sensor signal is less than self-test minimum. Possible causes for this fault are:
   • Open or grounded circuit.
   • Faulty CHT sensor.
   • Faulty PCM.

   Turn ignition off. Disconnect CHT sensor wiring harness connector. Inspect for damage and repair as necessary. Connect scan tester to DLC. Access CHT PID on scan tester. Turn ignition on. If PID voltage more than 4.6 volts, replace CHT sensor and repeat QUICK TEST . If PID voltage is 4.6 volts or less, remove jumper wire and go to next step. If scan tester is unable to access TP PID, go to next step.

8. 21) Check VREF Circuit Voltage  With TP sensor disconnected, turn ignition on. Measure voltage between VREF and SIG RTN terminals at TP sensor wiring harness connector. If voltage is 4-6 volts, go to next step. If voltage is not 4-6 volts, reconnect sensor and go to CIRCUIT TEST C.
9. 22) Check Signal Circuit For Short To Ground  Leave MD sensor and PCM disconnected. Turn ignition off. Disconnect PCM 104-pin connector. Inspect connector for damage and repair as necessary. Install EEC-V Breakout Box (014-00950), leaving PCM disconnected. Measure resistance between test pin No. 66 (CHT) and test pins No. 24, 51 (PWR GND), and 91 (SIG RTN) at breakout box. If each resistance measurement is 10,000 ohms or more, replace PCM and repeat QUICK TEST . If either resistance measurement is less than 10,000 ohms, repair circuit short and repeat QUICK TEST .
   NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 22) to step 90). No test procedures have been omitted.
10. 90) Continuous Memory DTC P1289 Or P1290  These codes indicate intermittent CHT sensor failure. Possible causes for this fault are:
    • Open or grounded circuit.
    • Faulty IAT or ECT sensor.
    • Low coolant level.
    • Faulty PCM.

    Turn ignition off. Connect scan tester to DLC. Access CHT PID on scan tester. Turn ignition on. While observing CHT PID, lightly tap on CHT sensor to simulate road shock. Wiggle sensor connector. A fault is indicated by a sudden change of CHT PID voltage. If fault is indicated, isolate and repair as necessary. If fault cannot be isolated, replace PCM and repeat QUICK TEST . If no faults are indicated, go to next step.

11. 91) Check Wiring Harness  With scan tester connected, and CHT PID still accessed, wiggle and shake small sections of wiring harness. A fault is indicated by a sudden change of voltage. If fault is indicated, isolate and repair as necessary. If no faults are indicated, go to next step.
12. 92) Check PCM Wiring Harness  Turn ignition off. Disconnect CHT and PCM wiring harness connector. Inspect connector terminals for damage and repair as necessary. If no faults are found, problem cannot be located at this time. Clear PCM memory and repeat QUICK TEST . If fault is found, repair as necessary and repeat QUICK TEST .
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 92) to step 100). No test procedures have been omitted.
13. 100) DTC P1299  This code indicates an engine overheat condition was detected by CHT sensor and fail-safe cooling strategy was activated by FMEM. Possible causes for this fault are:
    • Cooling system fault.
    • Low coolant level.
    • Engine mechanical fault.

    Locate cooling system fault and repair as necessary. Repeat QUICK TEST .