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Urgent - Fans not coming on

This is a discussion on Urgent - Fans not coming on within the General Help forums, part of the LSx Technical Help Section category; I have a 1998 Z28 (automatic) and about a week ago the fans stopped coming on. Now that the weather ...

  1. #1
    Junior Member
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    1998 Z28 Camaro

    Angry Urgent - Fans not coming on

    I have a 1998 Z28 (automatic) and about a week ago the fans stopped coming on. Now that the weather is getting hotter this is becoming a major issue. While the car is in motion the temperature stays about 185 or so and the A/C works great. When I come to a stop the temperature starts rising and the A/C starts cycling off and on again (due to freezing up - my Dad is an A/C guy). I know with these cars when you turn on the A/C both fans are supposed to come on, regardless of engine temp. Mine doesn't do that.

    The car is basically stock except for HPPIII programming P/N 380752). As a troubleshooting step I have removed the HPPIII programming and got no change. I have replaced the two gray fan relays with new ones from AutoZone. I have also replaced the coolant temperature sensor with a new one from AutoZone. Neither had any effect. I found, however, if I jumper a piece of wire from the two terminals on either of the relay sockets that are controlled by the relays the fans come on. Unfortunately they stay on even when the car is off.

    I performed all the tests in the Haynes manual in chapter 3 about verifying the fan circuit is working. All of the relays (the two original, 4-post, gray ones, and the one 5-post black one, and the two new gray, four-post ones) test good. I can hear them click on and off when I apply 12V to the correct terminals and the correct circuit is completed.

    I have an OBDII cable connected to my laptop running ScanTool. The check engine light has been on for this entire time and ScanTool lists the following codes:

    P0117: Engine Coolant Temperature Circuit Low Input
    P0118: Engine Coolant Temperature Circuit High Input

    The temperature sensor seems to show an accurate temperature reading so I'm guessing the new sensor (and the old sensor as well - tested with both) are good. I also, just for grins, jumped two of the the three wires coming off the temperature sensor harness and made the temperature show 280 degrees in ScanTool. The fans *still* did not come on.

    I can clear the codes but they just come back, which really doesn't solve the problem anyhow. I'm really stuck at this point and this is my daily driver to work. Any help would be greatly appreciated.

  2. #2
    Senior Member Danger731's Avatar
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    I'm no expert but since everthing is basically controlled by voltage maybe there is a voltage issue giving the pcm a signal it can't recognize ? To have a high and a low seems to point to a signal issue. Is there a way to check the signal the pcm needs ? Just a guess, G/L bro.

    worst comes to worse jump the fans like before and just instal a switch in you car so you can turn the fans off when it is not running.

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