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3800 and radiator fan probs by LoW_KeY
Started on: 11-15-2003 07:27 PM
Replies: 15
Last post by: Stinkin_V8 on 11-17-2003 05:06 PM
LoW_KeY
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Report this Post11-15-2003 07:27 PM Click Here to See the Profile for LoW_KeYSend a Private Message to LoW_KeYDirect Link to This Post
Well I never mentioned this before, but my lights and what not kept flicking while I was driving at night and the car shut off one time. My friend and I went up front and heard the relay clicking on/off and noticed it made my volt meter bounce from 18 down to 13.

We undid the relay/replaced the relay and it did the same thing clicking away making the volts bounce, well then we spliced a wire into it and grounded it out on a bolt by the headlight. The fan is constantly running now, and no more clicking from the relay or bouncing volt gauge.

I'm assuming its in the wiring somewhere? My friend said he emailed rockcrawl and asked about it, no response there anyone know what it might be? I mean I dont mind having the fan run all the time, but would like to fix the problem sometime

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88 5spd Modified 3800 Series II SC Formula
Modifications/2004 - Intercooler 3.0 pulley, 1 inch drop, interior

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Darth Fiero
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Report this Post11-15-2003 09:19 PM Click Here to See the Profile for Darth FieroClick Here to visit Darth Fiero's HomePageClick Here to Email Darth FieroSend a Private Message to Darth FieroDirect Link to This Post
Sounds like an electrical problem to me. If that fan relay was turning on and off rapidly it could have loaded the electrical system in such a way that caused the engine to stall.

There should be a green wire with a white stripe that goes to both the HVAC controls and the C500 connector. The stock Fiero engine harness has this green/white wire in it hooked to a temp switch on the engine. However, the 3800 computer has 2 fan outputs directly from the PCM so no temp switch is needed. Are you getting any trouble codes from the computer?

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LoW_KeY
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Report this Post11-15-2003 09:42 PM Click Here to See the Profile for LoW_KeYSend a Private Message to LoW_KeYDirect Link to This Post
not flashing no codes at me.. but like I said I cant get a scanner to work, I have a few more things to check that TK told me. That doesn't work I have a feeling I'll end up taking a long drive to who ever knows what they are doing, when it comes to ECM/Wiring I'm lost.

If I cant get nothing to show up on a scanner I would imagine that its cancelling out any lights that might flash?

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Darth Fiero
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Report this Post11-15-2003 10:35 PM Click Here to See the Profile for Darth FieroClick Here to visit Darth Fiero's HomePageClick Here to Email Darth FieroSend a Private Message to Darth FieroDirect Link to This Post
Well if you are using the 94-95 Bonneville computer there is no more trouble code flash function like the earlier GM cars had. You will need to have a scan tool to pull codes. Autozone offers a free code reading service they might be able to pull yours. How far away from Ft. Wayne, Indiana are you?
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LoW_KeY
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Report this Post11-15-2003 10:59 PM Click Here to See the Profile for LoW_KeYSend a Private Message to LoW_KeYDirect Link to This Post
be like I think a 3 hr a trip, pretty much right directly the middle of the mitten in michigan.
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topcat
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Report this Post11-16-2003 05:19 AM Click Here to See the Profile for topcatClick Here to Email topcatSend a Private Message to topcatDirect Link to This Post
I have the same problem with my fan running all the time. I have not pulled any codes yet, but will next weekend when I have a chance to work on the car. I have the SC38000 series II as well. I still have the stock relay in the fan circuit, but if this is wired to the ECM instead of a temp sender, I do not want to fart with it. The last thing I want to do is short out the ECM... Let me know what you find to be the problem. I will follow this closely. If I find the problem with mine, I will let you know.

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LoW_KeY
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Report this Post11-16-2003 06:35 AM Click Here to See the Profile for LoW_KeYSend a Private Message to LoW_KeYDirect Link to This Post
I'll keep you updated on what I find, granted this might fight against KR I'd like to hear others aspects towards it.

[This message has been edited by LoW_KeY (edited 11-16-2003).]

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Darth Fiero
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Report this Post11-16-2003 01:35 PM Click Here to See the Profile for Darth FieroClick Here to visit Darth Fiero's HomePageClick Here to Email Darth FieroSend a Private Message to Darth FieroDirect Link to This Post
Well topcat, the problem you might be having is the 3800 PCM has 2 outputs for cooling fans. If you have only hooked up one cooling fan relay, the PCM is going to want to see another relay on the other fan output otherwise it will flip out, set a code, and command both fans to operate all the time.

The 3800 PCM has it's outputs monitored by what is known as the Quad Driver Module circuit. Typically, 3800 computers have 3 quad drivers that are enabled to be monitored in the stock programming. The quad driver for the fan relays may also monitor say the A/C relay. When the PCM is not enabling say the hi fan relay, it will look to see if there is a B+ 12volt signal returning to the PCM from the relay (since the other side of the relay coil is hooked to ignition power). If it does not see this 12v return signal, it may flip a code for that quad driver module and activate all fan relays all the time and may not allow A/C operation. This is why you can't hook both fan outputs to the same relay. They need to both have seperate relays so the PCM sees the correct return signal if one is not activated.

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Stinkin_V8
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Report this Post11-16-2003 10:26 PM Click Here to See the Profile for Stinkin_V8Send a Private Message to Stinkin_V8Direct Link to This Post
Darth - D@amn, you are good...

Just to make sure I have this straight. I have one single speed fan in my Fiero, so I should hook the low speed output on the ECM to the "real" fan relay and hook the high speed output to a dummy relay, just so there is some amount of current draw on that line out of the ECM? By dummy relay, I mean a relay with no connections (in terms of the Bosch style relay) on the NO, NC or COM - just the line from the ECM connected to terminal 86 and a ground on 85.

Hope this isn't considered a hijack..

[This message has been edited by Stinkin_V8 (edited 11-16-2003).]

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Darth Fiero
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Report this Post11-16-2003 11:21 PM Click Here to See the Profile for Darth FieroClick Here to visit Darth Fiero's HomePageClick Here to Email Darth FieroSend a Private Message to Darth FieroDirect Link to This Post
 
quote
Originally posted by Stinkin_V8:

Darth - D@amn, you are good...

Just to make sure I have this straight. I have one single speed fan in my Fiero, so I should hook the low speed output on the ECM to the "real" fan relay and hook the high speed output to a dummy relay, just so there is some amount of current draw on that line out of the ECM? By dummy relay, I mean a relay with no connections (in terms of the Bosch style relay) on the NO, NC or COM - just the line from the ECM connected to terminal 86 and a ground on 85.

Hope this isn't considered a hijack..

[This message has been edited by Stinkin_V8 (edited 11-16-2003).]

Yes you can do that if you wish or even better you can do one of the following 2 things.

You can hook up another fan relay for the HI fan output that still turns on the fan. In effect you would have two fan relays hooked up in parallel but each one is activated by a different fan output.

Or you could hook up the low speed fan relay to a ballast resistor to the fan motor commonly found on GM cars equipped with the 3800. Then you would hook the hi speed fan relay up directly to the fan motor. This way the low speed relay would energize the fan motor thru the ballast resistor causing it to run a half speed. Then if the PCM requests hi speed it would be able to activate the hi speed relay to shunt full power to the fan. I like this way best because most of the time you don't need that fan running 100% to cool the engine. The lower speed fan function actually saves on the life of the fan motor, cuts down on battery drain, and allows the fan to operate quieter when in low speed mode.

Something else I just remembered, I don't know if I mentioned this earlier but getting back to the stock fan relay setup in the Fiero... Since the fan relay can be activated by the HVAC controls, when you would select an A/C function on the HVAC, the fan relay wire would be grounded thus turning on the fan. The problem is that if you have the 3800 PCM hooked straight to the fan relay wire then when the HVAC is in any A/C mode you would take the B+ 12v feedback away from the PCM. If the PCM is not commanding a fan on output at the same time, it might throw a Quad Driver Fault error like the one I was describing earlier thus turning the fan(s) on constant. Let me hunt down the GM description of how all this is supposed to work and I will post it here in a little bit.

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Darth Fiero
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Report this Post11-16-2003 11:54 PM Click Here to See the Profile for Darth FieroClick Here to visit Darth Fiero's HomePageClick Here to Email Darth FieroSend a Private Message to Darth FieroDirect Link to This Post

QDM #4 DTC P1670

CIRCUIT DESCRIPTION
The Powertrain Control Module (PCM) is used to control several components such as the A/C Relay, Malfunction Indicator Lamp (MIL), Low Speed Cooling Fan Relay and the High Speed Cooling Fan Relay. The PCM controls these devices through the use of a Quad-Driver Module (QDM). When the PCM is commanding a component "ON," the voltage potential of the output circuit will be "low" (near 0 volts). When the PCM is commanding the output circuit to a component "OFF" the voltage potential of the circuit will be "high" (near battery voltage). The primary function of the QDM is to supply the ground for the component being controlled. Each QDM has a fault line which is monitored by the PCM. The fault line signal is available on the data stream for display on the Tech 1 scan tool. The PCM will compare the voltage at the QDM based on accepted values of the fault line. If the QDM #4 fault detection circuit senses a voltage other than the accepted value, the fault line will go from a "low" signal on the data stream to a "high" signal and DTC P1670 will set.

DIAGNOSTIC TROUBLE CODE (DTC) P167O WILL SET WHEN
^ The engine is running.
^ The PCM detects an improper voltage level on a circuit connected to QDM #4.
^ The above conditions met for 5 seconds.

ACTION TAKEN (PCM WILL DEFAULT TO)
DTC P1670 does not illuminate the MIL. DTC P1670 could ground both fan relay outputs and disable A/C clutch relay operation depending on calibration.

DIAGNOSTIC AIDS
Monitor the voltage at each terminal shown above while moving related harness connectors including PCM harness. If the failure is induced, the voltage will change. This may help locate an intermittent condition. Check for bent pins at PCM and PCM connector terminals. If DTC reoccurs with no apparent connector problem, replace PCM.

As you can see, both fan relays as well as the A/C clutch relay and Check Engine light are monitored by the QDM4 circuit. If any one of these circuits have a problem, it could cause the PCM to go into default mode and fix the state of the outputs on the affected QDM circuit. Hope this info helps.

[This message has been edited by Darth Fiero (edited 11-17-2003).]

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Stinkin_V8
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Report this Post11-17-2003 10:21 AM Click Here to See the Profile for Stinkin_V8Send a Private Message to Stinkin_V8Direct Link to This Post
Darth, so you're saying the HVAC tries to trigger the fan relay via a switched ground, and the ECM does it via switched +12V, right? So one of those needs it's polarity switched, right? Here's a simple circuit that uses a Bosch relay to do that:

By the way, I "stole" this diagram from underthedash.com, they have a good section on relays and example circuits for anyone interested in relays.

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Report this Post11-17-2003 10:58 AM Click Here to See the Profile for topcatClick Here to Email topcatSend a Private Message to topcatDirect Link to This Post
Darth, where does the ECM get its signal to energize the relays? My fans was working fine until recently. The forward tranny mount bracket broke on my car, and the entire engine shifted. If the sender is on that side of the engine, it may have been damaged during the "shift". That is where I am going to start when I get the time. Otherwise, when can you take the car for diagnosis and repair
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Darth Fiero
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Report this Post11-17-2003 03:22 PM Click Here to See the Profile for Darth FieroClick Here to visit Darth Fiero's HomePageClick Here to Email Darth FieroSend a Private Message to Darth FieroDirect Link to This Post
Typically, all GM ECM/PCM's activate the GROUND side of the relays with 1 exception. Only the Fuel Pump Relay has 12+ supplied to it by the ECM/PCM. All other relays have fused 12+ IGN battery fed to them and the ECM/PCM turns them on by supplying the ground. In the case of the Quad Driver, when the ECM/PCM is not grounding the relay (to turn it on), it will be looking for 12+ IGN coming in on that circuit. This is what the QDM monitors.

Topcat, the PCM activates the cooling fan(s) based on the input of the coolant temp sensor. The PCM depends its grounds to the engine to activate the fan relays. If you had a couple of ground wires pulled or a ground strap come apart because of the broken mount, it is very possible this is what is causing your problem. The engine needs to be grounded to the chassis using some kind of wire or ground strap because the cradle is isolated by rubber mounts. I also think it is good practice to run an additional ground strap to the cradle to prevent static buildup from occuring.

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Darth Fiero
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Report this Post11-17-2003 03:33 PM Click Here to See the Profile for Darth FieroClick Here to visit Darth Fiero's HomePageClick Here to Email Darth FieroSend a Private Message to Darth FieroDirect Link to This Post
 
quote
Originally posted by Stinkin_V8:

Darth, so you're saying the HVAC tries to trigger the fan relay via a switched ground, and the ECM does it via switched +12V, right? So one of those needs it's polarity switched, right? Here's a simple circuit that uses a Bosch relay to do that:

By the way, I "stole" this diagram from underthedash.com, they have a good section on relays and example circuits for anyone interested in relays.

Actually here is a more appropriate diagram fitting the Fiero and how the cooling fan relay is wired stock.

The input (term 85) runs to both the HVAC controls and the stock temp switch (green/wht) wire. While this diagram is not entirely accurate, it shows us that a ground signal activates the relay and when the relay is activated, it sends 12v + Batt power to term 30 and out to the fan motor. The problem is that the stock Fiero HVAC controls will ground the fan relay input (85) which, if hooked directly to the 3800 PCM, would cause the PCM to lose the 12v feedback from the relay it is expecting to see if the PCM is NOT commanding the relay to be on.

In other words, when the relay is not grounded, you would get a 12v + reading from terminal 85 because the electromagnetic coil inside the relay would not be loaded, thus allowing 12v + to go straight thru from term 86 to 85, the two terminals the electro coil is connected to.

Same thing happens with a light bulb. If you supply 12v + to one side of the buld and don't connect the other side of the bulb to ground, you would read 12v + on both sides of the bulb with a digital volt meter. The 3800 PCM has this same capability. This is the function of the QDM circuit. It monitors the outputs of the PCM when they are NOT active to check to see that these circuits are intact.

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Stinkin_V8
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Report this Post11-17-2003 05:06 PM Click Here to See the Profile for Stinkin_V8Send a Private Message to Stinkin_V8Direct Link to This Post
That makes perfect sense.. Once again, thanks for the Wiring 101 course. I was sort of wondering what I would do with these two outputs from the ECM, and probably would have only hooked up one of them.

You just sent my chip back to me last week, so that's right about where I'm at on the project. Perfect timing.

Keep up the good work, Darth.

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