96 Regal Cooling fan circuit issue

[btbutts]

Hi, I have a 1996 Buick Regal Gran Sport with the 3800 Series 2 engine. I just recently rebuilt both the top half of the engine (heads and up) and the transmission and both are running strong... it's shifting quickly, firm, and getting though the gears 😀😀

The cooling fans never worked since I bought the car 3 years ago. I'd really like to get my A/C working again but there is no point until the fans are running since those fans are also used by the A/C system, especially while at an idle.

So to cut to the chase, here is where I'm at. I have done everything in this order, trying to narrow the problem down.

I have a check engine light on (P0113 - Intake Air Temp Sensor 1 Circuit High Input) - which I know tells the ECU that the air is colder than it actually is. (As the air temp increases, the voltage decreases). This is failed because it is showing up too high to the ECU, exceeding 5V and representing cold air. I think it got damaged when removing the Air Box assembly. Probably just need a new sensor here but according to the repair manual, this sensor is not in the circuit for cooling fan operation.

I have a Haynes manual and I've been using it to follow the circuits. My car uses the Manual Cooling Fan circuit (only 2 relays). Both relays are identical and are also identical to the ignition relay. I swapped each cooling fan relay into the ignition relay terminals and the car started every time. Relays are good.

The coolant temperature switch is new. I replaced it when I rebuilt the engine top half as the exhaust crossover pipe had melted it's connector.

Using a grounded test light, Pin 30 lit up on both Cooling Fan relay terminals. So I'm getting power. Using a multi-meter, it tested 12.48V with the car off and 13.6V to 13.7V with the car on.

Now knowing there is power, I used a jumper wire on fan relay 1 terminals 30 and 87 (with the relay removed from the fuse box of course) and the fan cut on. I did the same procedure on fan 2. The fan cut on. So I know that power is able to be sent to the fan and it operate, all motors are good!

The repair manual shows that the primary fan relay will show constant power on terminal 86 with car on or off. I tested with a multi-meter and it matches the results of fan relay 1 pin 30 test.

On relay 2, pin 86 will only show power with key at on position. I tested the terminal with Key on Engine off and Key on Engine on and it matched the results of the pin 30 relay 2 test.

Now this only leaves pin 85 which leads to the ECU. I know that these wires, dark green (high speed control) and dark blue (low speed control) from the battery will always show current until the ECU grounds them to activate the relay and therefore the coolant fans. I followed both wires back through the wiring harness, to the ECU and replaced them with new sections of wire.

After reinstalling everything back into it's place, the secondary fan started running after I started the car and let it reach operating temp. That's always a good sign 🙂

However, the following day, I wanted to replicate the success of my repair. So I started the car and went for a drive, came home and let it idle until hopefully the fans come on. They didn't. I know people will say to plug in an OBD2 reader and check the live data to see the actual real time temp of the engine but every reader I have ever plugged into this car has never populated the coolant temp field. This forces me to use the dummy light. UGH!

I will say the ECU is new, my last computer was literally stuck in limp mode (Even after 4 months of no power), it would not go into relearn mode and it fried when the transmission went out so I replaced it.

I did take the car to a parts store and I am now getting a new code. P0481 (Cooling Fan Relay 2 Control Circuit).

I tested Pin 85 on both relays with the car DEFINITALY at operating temp if not over normal operating temp (I drove it like mad and let it idle, continuously revving the engine for a while) and it shows .06V with a multi-meter. It never drops the current any lower to ground out the relay.

Could the set codes cause the computer to seize all fan operation?
Could the set code for the Air Temp Sensor cause the fans to stay off because it thinks the air is cooler than it really is?

What are my next steps? At this point, I'm lost. I feel like I am capable of this repair. I have rebuilt everything on this car personally except for welding on the new catalytic converter... I HATE exhaust work!!! lol I even tore down and rebuilt the 4t60e transmission with the Sonax and TransGo shift kits and updated clutch pack designs. I don't get why some electrical problem is kicking my A$$!! 😕

I could sure use some help on this. Thanks 🙂

 

[92sub]

Lets do small bites here:
The Air Temp sensor code has no bearing on the fans. Also your miss-understanding the ECU response to the bad circuit/sensor. Once the code sets for the high voltage the ECU KNOWS the data is faulty and no longer uses it during operation. Instead it uses a 'default' value from a look-up table that is based on different inputs. This look-up table data isn't very accurate and air temp is fairly critical for proper fuel trim so I'd fix this sooner rather than later.

 

[92sub]

The fans are designed to come on at VERY high temperatures. On your vehicle they should come on at about 212 degrees. When you have a thermostat of 195 it can take a LONG time to build enough heat to get to 212. It was not uncommon for me to leave a vehicle idling for 45 minutes in hot weather before the fans would come on.....longer or even impossible in cooler weather. So I'm trying to say you might not have any issue at all. You never mention OVER-heating....you just expect the fans should be running and it might just not be hot enough for them. You'd need a TECH2 scan tool to test properly. With a TECH2 you can see the coolant temp the ECU sees and also command the fans to run to test ECU control of them.

And finally I think you set that P0481 during your testing.....clear the codes and see if it comes back......and fix that Air Temp code too!

 

[btbutts]

Hi guys! Thanks for the replies.

I went back and tested the wires I had replaced from the ECU to the fusebox by removing the connector from the computer and testing between the ECU connector pin and the relay terminal. Both wires tested good! I now know the wiring to both relays from the ECU is good. The wiring to the fan from the relay including fan ground is good. lastly I know that both "hot" wires to the relay are good. It seems my wiring is fine here. I ruled out the relays themselves being the culprit when I swapped each of them into the ignition coil relay slot and the car started every time.

I replaced the Intake Air Temp sensor as stated in my first post, it was faulty.

After all the above, the ECU obviously reset because it had no power. I drove the car and 120 miles later, I have no SES light. 🙂

The bad news is the fans still do not operate. So I need to dig a little deeper and think. Remembering the "nature" of the original coolant temp sensor, the dummy light and gauge on my instrument cluster showed the normal operating engine temp at 1/4 and not to exceed this too much even during warmer months. To add to this, I watched a video on YouTube one time with a guy showing off his 96 regal (same engine) and you could see his coolant temp gauge only at the 1/4 mark and he was revving/driving it pretty hard... I only mention that video so that I can compare the behavior of my car to others of the same model and year. Anyways, the new sensor shows a normal operating engine at the 1/2 mark (guess this is why you don't judge temp by a dummy light) which to be honest I like because I can get a better idea how the car is warming up especially in the colder months (almost like a countdown of sorts to see when I get some warm air 😀 ). The last sensor worked, it still would if I didn't through it away. It just had a connector that melted off from the metal part of the sensor. I used to have to clip it's connector housing to the wiring harness and slide that over the three metal prongs on the sensor (wire contacts). This is why I replaced it. But I think however that the new sensor is not displaying readings as appropriate for my car. I am going to replace both the sensor again and there is a section of wire, an extension really, it's about a foot long from the sensor to it's connector on the vehicle wiring harness, I'm going to rewire it in case the wire is just brittle from the exhaust crossover pipe just below it.

I'll post the results when done. Thanks 🙂