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2004 Chevrolet Trailblazer Question: Thermostat location and what tools do I need?

 

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Due76x, Wayne, MI, August 04, 2011, 23:44
 Rookie

Engine light on, OBD II Code P0128 and P0106.
Coolant temperature below Thermostat. Leak somewhere from the coolant line when the air-cont on. I just change the map sensor last week and reset it but now the engine light back on. Should I have to change the Thermostat?
I really appreciate any help...

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  • Answer #1

    August 05, 2011, 23:39
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     Journeyman

    for p0128, you can try :
    Verify coolant strength & level
    Verify proper cooling fan operation (check if it's running more than it should). Replace if necessary.
    Verify proper engine coolant temperature (ECT) sensor operation, replace if necessary.
    Verify proper intake air temperature (IAT) sensor operation, replace if necessary.
    If the above items check out good, replace the thermostat
    If Nissan vehicle, check for Technical Service Bulletins (TSBs), as the ECM may need to be reprogrammed to correct the P0128 code.
    for p0106
    Using a scan tool, watch the MAP sensor value with the key on, engine off. Compare the BARO reading with the MAP reading. They should be roughly equal. The voltage for the MAP sensor should read approx. 4.5 volts. Now start the engine and look for a significant drop in the MAP sensor voltage indicating the MAP sensor is working.

    If the MAP reading doesn't change perform the following:

    With the Key on, engine off, disconnect the vacuum hose from the MAP sensor. Using a vacuum pump, pull 20 in. of vacuum on the MAP sensor. Does the voltage drop? It should. If it doesn't inspect the MAP sensor vacuum port and vacuum hose to manifold for a restriction of some kind. Repair or replace as necessary.
    If there are no restrictions, and the value doesn't change with vacuum, then perform the following: with the Key on and engine off and the MAP sensor unplugged, check for 5 Volts at the reference wire to the MAP sensor connector with a Digital Voltmeter. If there is none, check for reference voltage at the PCM connector. If the reference voltage is present at the PCM connector but not the MAP connector, check for open or short in the reference wire between MAP and PCM and retest.
    If reference voltage is present, then check for existing ground at the MAP sensor connector. If it isn't present then repair open/short in the ground circuit.
    If ground is present, then replace MAP sensor.

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