jason331

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.

EnfuegoZ28

I think there is a fan switch near the fan motors that tells the fans when to come on. Make sure this switch is working properly because it sounds like this switch is bad. Just a thought.

h82goslo

I have the same issue with mine and I dont recall a "fan switch" being around the fans? Maybe wrong need more responses please.

sixvi6-camaro

iTrader: (9)

you only replaced 2 relays? The way the fans work differently than expected in these cars. There is a relay for fan 1 and another for fan 2 but.. fan 3 also controls the fans as well. how is works is when the low fans kick on the 3rd relay runs both fans in series so each fan gets 6v running at a low speed. High fans runs them in parallel so they both get full 12v. Exactly how that is wired I have no idea because every book I've looked at for these cars has no mention of this. I discovered this from manually triggering all 3 relays and fans in different combinations and looking at the voltages. bottom line replace the relay labeled fan 3.

bluehawk2

iTrader: (74)

Do you have a slp fan switch? I had probs with my fans and it turned out to be the slp fan switch.

2001NBMZ28

Are you throwing the same ECT codes as the original poster? If the SES is on get them read, yours could be a totally different issue - there are DTCs specifically for the fans.