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P0118 code after repairing blown head gasket

Tiny
DH44
  • MEMBER
  • 1999 CHEVROLET MALIBU
  • 3.1L
  • V6
  • 2WD
  • AUTOMATIC
  • 295,000 MILES
After repairing the blown head gasket, I have a check engine light with code P0118. The temperature gauge needle does not move after the engine warms up. I replaced the temperature sensor and still have the same issue. There is approximately 5 volts at the sensor harness connector.
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Thursday, July 26th, 2018 AT 7:47 PM

3 Replies

Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Good morning.

There are two sensors for the coolant temperature. One is for the computer to control fuel and one is for the gauge.

The one in the front top of the motor is for the PCM for fuel control. The gauge is on the back cylinder head toward the rear of the engine. It has a single wire to it. I believe it is a green wire.

Check and see if there is any voltage to that wire.

Roy
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Friday, July 27th, 2018 AT 5:34 AM
Tiny
DH44
  • MEMBER
  • 2 POSTS
I do not see the second sensor on this particular engine. I tested the sensor at the back of the head (front head, or left hand side, whichever you want to call it) again. I have 4.97 volts at both of the wires while connected to the sensor with ignition on and with engine running. The voltage value on the ground side does not drop as the coolant warms up. I measured the resistance across the temperature sensor as it was warming up, and I saw the resistance doing down as it got warmer. Does this mean I have a grounding issue? If so, can I simply splice into the ground wire and ground it in a new location rather than tracing the circuit back to its origin?
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Monday, July 30th, 2018 AT 7:15 PM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Both wires go to the PCM. There is a five volt feed and the return is what the PCM reads to control the fuel mapping.

Do not splice into anything. The signal return should vary according to temperature. If it does not, either there is no coolant in the manifold to change the reading or the sensor is no good.

Roy
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Tuesday, July 31st, 2018 AT 3:05 AM

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