Coolant Temp (sender?) Problem

Everything points to the coolant temp sender. At 45 seconds after starting my 2003 3.4 from a cold start my temp pointer goes from bottom to top of gage. I'm guessing grounding out then. Engine definitely not hot in 45 seconds. I can touch the exhaust manifolds. But why 45 seconds, and always 45 seconds., and not as soon as I start? Is got to be related to onboard diagnostics? Guess I've got to invest in a code reader.

 

I believe it's on the back of the left cylinder head. It will have only one wire there is a different one for the engine management that one has nothing to do with the gauge. When it's reading hot remove the wire the gauge should return to dead cold if so replace the sensor.

 

I'm definitely no expert but your thermostat may have failed. They open up when they get hot and they are designed to fail in the open position.

 

Trouble Code: Print this code data

Number of Trips to Set Code: 1

• CCM Details
• MIL Details

Trouble Code Conditions:
California Models ECT sensor less than 19.4 degrees F, engine started, engine runtime over 20 minutes, and the PCM detected the ECT sensor indicated 68 degrees F or less; or with the ECT sensor from 19.4 degrees F to 50.0 degrees F at startup, engine runtime over 5 minutes, the PCM detected the ECT sensor indicated 68 degrees F or less; or with the ECT sensor more than 19.4 degrees F at startup, and the engine runtime over 5 minutes, the PCM detected the ECT sensor signal was 68 degrees F or less; or with the ECT sensor over 50 degrees F at startup, engine runtime over 2 minutes, the PCM detected the ECT sensor signal did not reach 86 degrees F during the CCM test period.

Possible Causes:

• * Check the operation of the thermostat (it may be stuck open)
  
  
• * ECT sensor signal circuit has high resistance
  
  
• * ECT sensor has failed
  
  
• * Inspect for low coolant level for an incorrect coolant mixture
  

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Listen
Trouble Code: Print this code data

Number of Trips to Set Code: 2

• CCM Details
• MIL Details

Trouble Code Conditions:
Engine started, ECT sensor signal below 140 degrees F at startup, and the PCM detected the ECT sensor did not reach 167 degrees F after the warmup period expired (engine runtime 5-10 minutes).

Possible Causes:

• * Check the operation of the thermostat (it may be stuck open)
  
  
• * ECT sensor is out-of-calibration or skewed
  
  
• * Inspect for low coolant level or for an incorrect coolant mixture
  

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The sender for the dash gauge is on the rear of the lower intake manifold, red arrow.
The "engine coolant temperature" used only for engine management is at the front, blue arrow.

 

ETC has no effect on temp gauge.

His exhaust manifold is cool enough to touch gauge reads full hot after less than minute.

 

Thanks "Dirty Pool". I figured a setup as you pointed out. My incorrect Haynes manual showed a single sensor on the lower intake, halfway between front and rear. I probably would have never found it since it's covered by a plastic case. Sensors, yuck. I miss the old days... 8 plug wires, 1 fuel line and 500HP.

 

Yeah, nothing to do with thermostat. But, thanks for the inputs, all. Tacomaworld rocks!