New Engine Is In Fan's Not Working

[DierDesire824]

Alright we got the new engine in and wired up yesterday. Started right up then we go through the typical bleeding of the coolant system and overheating problems for about a half hour. Then when done we take it for a drive find out we didn't tighten some hoses hook them all back up then notice the fan's aren't kicking on.


What could cause the fan's to not kick on at high temp the temp gage is working cause I can watch the temp on the dash. Also, the fan's are wired up. Before I used to be able to turn on the AC and that would turn the high speed fan's on now even with the AC on the fan's don't click over.


1997 Camaro Z28 New Installed Longblock stock internals. Pacesetter long tubes , ORY Y-Pipe, Accel 30# Injectors, MSD Super Conductor Wires, NGK Iridium IV Plugs, MSD Cap and Rotor, Borla Cat Back

[Joe 1320]

I would first use a digital volt meter to determine if power is at the harness connections to the fans themselves, then check the relays and fuses in the fusebox under the hood.

[Injuneer]

Scan the PCM. That will tell you if the relays are accepting the commands from the PCM. If there are no codes for the relays, check to make sure you have continuity on the +12V load side of the relay, and that the fans are plugged in.

The gauge and the PCM use two different sensors. A faulty coolant temp sensor in the water pump housing could set a code, or it might just be damaged enough not to show the correct coolant temp. Again, get a scanner on it and see what temp the CLT sensor is sending to the PCM.

[Rob B (shoebox)]

On a fresh fill of the cooling system, the air is not often completely purged. This seems to cause localized heating or maybe steam pockets and the temp sensor in the head may report very high temps. The temp sensor in the water pump may not be seeing this same temp and hence will not command the fans on. Bottom line is, get all air purged from the cooling system (and check temp readings by the PCM as Injuneer suggested).

[DierDesire824]

I checked the car with my laptop and tekmate scanner and the coolant tempature reading graph was working and was also around where the gauge was. Thanks to the cold weather I still can drive it around and it doesn't heat up it stays around 180 - 190.

Also, my ignition timing advance for #1 is 15 I just got long tube headers and have not put on a lt4 knock module is that timing advance very high on my other engine i remember it being at zero. Although I might be remembering something else.

Also looked under the hood at the fusebox and one of the black boxes is missing it's on the right side and the middle one of the big boxes. Would tell you guys what the fuse or relay box says it's called but when i bought the car it did not have a fuse box cover.

[DierDesire824]

Test Fans

You can jumper two pins on the DLC that should cause the fans to come on. 1993-1994 cars with the 12 pin DLC can jumper pins A and B. On a 1993, that is the same way that you would retrieve trouble codes from the ecm. The 1994 won't give you any codes, but the fans will engage. 1995-1997 uses pins 5 and 6 on the 16 pin DLC to initiate what is called "field service enable mode". That will cause the fans to come on and operate most sensors for sanity checking. After placing the jumper on the correct pins, turn the key to ON (don't start). If the fans work after jumpering the DLC, your PCM is capable of operating the fans and all fan wiring/relays should be ok.

I found that in another thread searching the board. Can anyone further explain this procedure I also googled it and couldn't find any pictures.

I am guessing that it means take a pin and connect pins 5 and 6 ? where are these pins ?

[97LT1Z28]

I replaced my motor recently and the same exact thing happened to me . . . .When I got the car back, the fans wouldn't kick in at all. They would stay on low if I had the A/C on but on hot summer days, this wasn't enough to keep the temp from creeping up.

I could not find what was causing it, so I installed the SLP Fan control. This allows you to control the fans manually without interupting stock operation. Whenever I see the temp creeping up, I turn the fans on high and bring the temp back down - works like a champ and it was a quick fix.

Several mechanics told me this is a common "short" that happens in 95-97 model LT1's.