Compression Ignition Addict
Join Date: Dec 2007
Thanked 311 Times in 300 Posts
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OK First, don't look for the AIH to come on, they Rarely do and not important to starting.
Second, the GPR is regulated mostly by the EOT (Engine Oil Temp) sender to know GPs are needed.
The PCM sends a ground path to the GPR to activate it. Be sure it's doing that by removing the two sm terminals from the relay. One will have 12v in it, the other should switch to ground for as long as the PCM thinks wants the GPs on (this varies with temp and has NOTHING to do with the WTS light.
And yes, once the PCM is satisfied that the EOT is warm enough, even though the WTS comes on, it doesn't send that ground path to the relay.
If the relay checks-out (the most common cause) what's left is the EOT sensor, the PCM, or the wiring & plug between them (both from the sensor & to the relay, with the PCM in between)