Mechanics

CHEVY ERROR CODE P0118

2001 Chevrolet Blazer

Engine Cooling problem
2001 Chevy Blazer 6 cyl Four Wheel Drive Automatic 109000 miles

What do I look for under this error code?
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Aprilrein
February 11, 2010.




Hello,

Below is code def and testing.

DTC P0118: ENGINE COOLANT TEMPERATURE SENSOR CIRCUIT - HIGH VOLTAGE

NOTE: Circuit Description Code Enable Criteria

Conditions for running DTC: " Engine has been running for more than 60 seconds.

Conditions for setting DTC: " ECT sensor temperature is less than -36 F (-38 C) for 20 seconds.

Diagnostic Procedures

" Engine has been running for more than 60 seconds.
" ECT sensor temperature is less than -36 F (-38 C) for 20 seconds.

Page 1 of 2
Engine Coolant Temperature (ECT) sensor is a variable resistor, sometimes called a thermistor, that measures temperature of engine coolant. The PCM supplies 5 volts to ECT signal circuit. When ECT is cold, sensor resistance is high. When ECT increases, sensor resistance drops. With high sensor resistance, PCM detects a high voltage on ECT signal circuit. With lower sensor resistance, PCM detects a lower voltage on ECT signal circuit. If PCM detects an excessively high ECT signal voltage, which is a low temperature indication, this DTC will set.

1. Perform powertrain diagnostic system check. See POWERTRAIN DIAGNOSTIC SYSTEM CHECK under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.

2. Using scan tool, observe ECT sensor temperature. If scan tool indicates that ECT sensor temperature is less than -36 F (-38 C), go to step 4. If scan tool does not indicate that ECT sensor temperature is less than -36 F (-38 C), go to next step.

3. Observe the FREEZE FRAME/FAILURE RECORDS data for this DTC. Turn ignition off for 30 seconds. Start and operate vehicle within the conditions for running the DTC or as close to FREEZE FRAME/FAILURE RECORDS data. See CODE ENABLE CRITERIA. If DTC resets, go to next step. If DTC does not reset, see DIAGNOSTIC AIDS.

4. Turn ignition off. Disconnect ECT sensor harness connector. Connect a fused jumper wire ECT sensor harness connector terminals. Turn ignition on, with engine off. Using scan tool, observe ECT sensor temperature. If scan tool indicates that ECT sensor temperature is greater than 280 F (138 C), go to step 7. If scan tool does not indicate that ECT sensor temperature is greater than 280 F (138 C), go to next step.

5. Turn ignition off. Connect a fused jumper wire between a known-good ground and ECT sensor harness connector terminal " B" (Yellow wire). Turn ignition on, with engine off. Using scan tool, observe ECT sensor temperature. If scan tool indicates that ECT sensor temperature is greater than 280 F (138 C), go to step 7. If scan tool does not indicate that ECT sensor temperature is greater than 280 F (138 C), go to next step.

6. Turn ignition off. Check for short to voltage, high resistance or open in Yellow wire between ECT sensor and PCM. Repair as necessary. After repairs, go to step 12. If circuit is okay, go to next step.

7. Turn ignition off. Check for high resistance or open in Black wire between ECT sensor and PCM. Repair as necessary. After repairs, go to step 12. If circuit is okay, go to step 9.

Note: If a short to a separate voltage source occurs, this DTC may set and damage the ECT sensor. If this condition is present, perform a continuity test to all other PCM circuits to diagnose the specific fault. See WIRING DIAGRAMS.

8. Check for poor connections at ECT sensor harness connector. Repair connections as necessary. After repairs, go to step 12. If connections are okay, go to step 10.

9. Check for poor connections at PCM harness connector. Repair connections as necessary. After repairs, go to step 12. If connections are okay, go to step 11.

10. Replace ECT sensor. After replacing sensor, go to step 12.

11. Replace PCM. Perform PCM relearn procedure. See POWERTRAIN CONTROL MODULE under PROGRAMMING. After replacing PCM, go to next step.

12. Turn ignition on, with engine off. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Operate vehicle within the conditions for running the DTC. See CODE ENABLE CRITERIA. If DTC runs and passes, go to next step. If DTC resets, go to step 2.

13. Using scan tool, observe the stored information and Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See DIAGNOSTIC TROUBLE CODE DEFINITIONS. If no DTCs are displayed, system is okay.

Diagnostic Aids

If a short to a separate 5-volt source occurs, this DTC may set. If this condition exists, test to all other PCM circuits to diagnose the specific circuit. After starting engine, the ECT should rise steadily to about 194 F (90 C), then stabilize when thermostat opens.

Check ECT sensor at various temperature levels in order to evaluate the possibility of a skewed sensor. See appropriate SENSOR OPERATING RANGE CHARTS article. A skewed sensor could result in poor driveability concerns. If a malfunction is not present at this time, refer to DTC P1115.

.

Obxautomedic
Feb 11, 2010.


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