Cooling fan circuit

[supercrackerbox]

The car is a 1986 Daytona Turbo Z with a TII conversion.

My cooling fan won't come on. I've got a code 35. With the engine running, I can disconnect the coolant sensor and nothing. Swapped the relay and no go. I have perfect conductivity on the ground and power wires, and the fan works when I hot wire it.

I borrowed Ray's OTC scanner to see what that would tel me. The scanner keeps saying no fault codes, but the OBD still says 35 and 22 (coolant sensor unplugged). The Factory diagnostic manual says to put the scanner in ATM test mode before beginning tests, I can't find anything like that on the menu, so I don't know if the voltage tests are reading correctly or not. I also don't know if I'm supposed to have the engine running, just have the key on, sacrifice a goat, or what. Next step is to disconnect the red connector on the LM, which of course I'm wary of doing even with power hooked up, much less with the key on, but it seems to be leaning towards a faulty logic module.

I'm lost on this one.

[supercrackerbox]

Okay, now I figured out how to get the scanner to read the codes. Not that it actually gets me anywhere . . .

[slasky]

I could be the wire that goes from the LM to the fan relay. Test it with an ohm meter.

[midohiomoparsource]

Maybe a dumb suggestion, but what if you turn the defrost on? Does it turn on then? Maybe you are losing power to the fan itself even though it shows there when relay closes somewhere.

If not, I would guess LM as well.

Matt

[supercrackerbox]

Well, I had to do a little bit of driving around on Saturday, and it was cold and raining, so the defrost was on, and no change.

Slasky, I'm still planning on trying your idea, just didn't get a chance since it was raining all day Saturday and yesterday we had to install a new water heater in the house.

Crazy question: I think I've still got an '86 LM laying around somewhere. Even though this car is now TII, would I still be able to plug it in and get the car to idle enough to see if it changes the condition?

[mcsvt]

As long as it's TI 2.2 to TII 2.2 it "should" idle on the old cal... Never tried it myself, but was told it would work. I need to plug in my T1 SMEC to try something on my TII, both are 2.5 so it "should" work for me as well.

[cordes]

The wiring for the 86 TI cal and the 87 TII cal are very different. If it does work, I would be suprised if it worked well. Have you checked to see that you are getting power to the relay when the fan should be on?

[mw6886]

It is possible that the LM has a bad chip on it. (Obviosly the chip that controls the relay that controls the fan.) About middle left there are two chips that are "relay" chips. If the fan is not coming on, and it is not a wiring or relay problem, its probably the bottom chip that has gone bad.

To get the 86 LM to work, you'll just need to get the map wiring converted over. The other two changes are inconsequential.

To get more technical, you can test those chips out. The 4 middle pins are ground. If you use a DVM, you can see a short from ground to pin if bad.

[supercrackerbox]

I could be the wire that goes from the LM to the fan relay. Test it with an ohm meter.

No resistance, good circuit.

The wiring for the 86 TI cal and the 87 TII cal are very different. If it does work, I would be suprised if it worked well. Have you checked to see that you are getting power to the relay when the fan should be on?

Swapped it in, idled suprisingly well. No change in condition however, and no fault codes whatsoever (which is very odd considering the MAP was unhooked). Results inconclusive. Question: Which wire am I supposed to test for power? The blue/pink one that goes to the LM, or the fat grey one that runs thru the fusible links? Fusible link *appears* to be fine BTW, but I am hesitant to probe it as that invariably damages it. If I test for resistance from the fat grey wire to the positive battery terminal, what should my result be? It starts out at 0.8 ohms and increases to 9.82 ohms over a period of about 5 seconds. Mulitiple times I got the same result.

To get more technical, you can test those chips out. The 4 middle pins are ground. If you use a DVM, you can see a short from ground to pin if bad.

What's a DVM? No, the last thing we need to do is get more technical, this is all pretty greek to me. More likely we should look at this like I'm an 8 year old.

[supercrackerbox]

Oh, and I also figured out what the ATM Mode on the diagnostics scanner is supposed to do- cycling the circuit on and off while you run the tests, however I still have not figured out how to engage that mode with this particular scanner.

[mw6886]

No resistance, good circuit.




Swapped it in, idled suprisingly well. No change in condition however, and no fault codes whatsoever (which is very odd considering the MAP was unhooked). Results inconclusive. Question: Which wire am I supposed to test for power? The blue/pink one that goes to the LM, or the fat grey one that runs thru the fusible links? Fusible link *appears* to be fine BTW, but I am hesitant to probe it as that invariably damages it. If I test for resistance from the fat grey wire to the positive battery terminal, what should my result be? It starts out at 0.8 ohms and increases to 9.82 ohms over a period of about 5 seconds. Mulitiple times I got the same result.



What's a DVM? No, the last thing we need to do is get more technical, this is all pretty greek to me. More likely we should look at this like I'm an 8 year old.

DVM = Digital Volt Meter, probably what you are already using for your Ohm meter.
You should probably also be checking for voltage at the fat grey wire to the positive battery terminal. Testing for resistance (ohms) means nothing there.

[supercrackerbox]

DVM = Digital Volt Meter, probably what you are already using for your Ohm meter.
You should probably also be checking for voltage at the fat grey wire to the positive battery terminal. Testing for resistance (ohms) means nothing there.

Duh, yeah, that's what I'm using. Told you I'm a noob at this. I get 13.46 volts at the fat grey wire. So I'm getting power to the relay, there's no blockage of power from the LM to the relay or from the relay to the fan, so for whatever reason, the relay is not closing. Either the relay is still bad, or it's still the LM.

[slasky]

Check for + voltage at the dark blue and pink wire on the red connector at the logic module when the engine is on and the cts is unplugged.

[supercrackerbox]

Check for + voltage at the dark blue and pink wire on the red connector at the logic module when the engine is on and the cts is unplugged.

Nothing.

[slasky]

Nothing.

Sounds like you LM is not working. Is there a dark blue and pink wire at the relay?

[supercrackerbox]

Yep, and perfect continuity between the relay and the LM.

Ray is coming over, we're going to try one more relay (off his car so we know it works) and another LM that he has since the one I tried gave no codes at all. I'll post my findings.

[slasky]

Unplug the LM and apply + 12v to the dark blue and pink wire. The relay should click if it is good.

[supercrackerbox]

Okay, everybody get ready to point and laugh.

A week or so ago I installed a BOV on my lower intercooler hose. In doing so, I knocked the connector off of my reverse light switch on my transmission, and broke one of the tangs off.

While tracing the wiring diagram to the relay, there are six wires. The fat grey wire which supplies power to the relay, the green wire which goes to the fan, a black/white wire that goes to the AC compressor, the blue/pink wire to the LM, a blue/black wire which connects to the WOT relay (which kills the AC and turns on the fan), and a white wire which goes to a seven pin connector where it is spliced to another white wire which goes to (drum roll) . . .

The reverse light switch.



I spent five days on this car, it took Ray 15 minutes to tell me, without even looking, that the #2 fuse under the dash was blown.

[cordes]

Okay, everybody get ready to point and laugh.

A week or so ago I installed a BOV on my lower intercooler hose. In doing so, I knocked the connector off of my reverse light switch on my transmission, and broke one of the tangs off.

While tracing the wiring diagram to the relay, there are six wires. The fat grey wire which supplies power to the relay, the green wire which goes to the fan, a black/white wire that goes to the AC compressor, the blue/pink wire to the LM, a blue/black wire which connects to the WOT relay (which kills the AC and turns on the fan), and a white wire which goes to a seven pin connector where it is spliced to another white wire which goes to (drum roll) . . .

The reverse light switch.



I spent five days on this car, it took Ray 15 minutes to tell me, without even looking, that the #2 fuse under the dash was blown.

I did not even think of that. I should have thought of that for sure. glad you figured it out.

[MiniMopar]

Yeah, the 86 is goofy. They grabbed 12V from the backup lamp circuit to power the relay coil.