need mustang help

RodneyWright · **Posted:** Tue May 12, 2015 1:19 pm

DickRasmussen wrote:

Rodney - Were those readings with the low speed relay out of the socket but with ignition on? Yes, ignition on w/ the physical relay out. If so that is what I expect is "correct". .02 volts is essentially "zero" in this situation due to meter calibration and maybe a little bit of "above zero volts" from the PCM.

I'm not sure whether the PCM is supposed to connect pin 86 to ground with the ignition on but the engine not running.

Can you disconnect the wire between pin 86 and the PCM? If so, with the relay in the socket try applying chassis ground to the connector that the contact that you removed the PCM wire from with ignition on. The relay "should" then apply power to the fan. I'm reluctant to suggest applying ground to 86 with the PCM connection intact even though my "guess" is that ground won't hurt the PCM. I just don't know enough to be sure and I wouldn't risk my $$$ let alone yours. No, I can't easily disconnect the wire from the underside of the fuse block. I'm not sure how they are locked into place. As I had mentioned earlier, there seems to be a "middle layer" between where the fuse plugs and how the underside blades engage the wiring harness. Some of the fuse layout make no sense if you look at the fuses vs the bottom side wiring.

Remember even if you have to spend even a $1000 for diagnostics and a new PCM the cost of trading to something else and setting it up will be much more IF you otherwise would like to keep this car. :wink:

Yup, there is truth in that....

comments above....

George Bright · **Posted:** Tue May 12, 2015 7:38 pm

RodneyWright wrote:

diving deeper....

After closer inspection of the BEC or fuse box layout, it looks like terminals 85-86 are flip flopped between the high speed and low speed relays. I was only looking at the bottom of the relay for the markings, so I gave bad info before.

In retesting the low speed 85-86 terminals, 85 gives a 12v reading grounded w/ the key on. Interesting enough 86 measures .02v. What does this corrected info mean?

Is that with the relay pulled out? with the relay out i would expect it to be 0v. With the relay in place I would expect it to be 12V. The PCM grounds the 86 terminal when it wants to run the fan. If you jumper the 86 terminal to ground with the relay in place it should bring on the low speed fan.

You don't want to drive around with the low speed fan jumpered on because the fan is a 2 winding motor and it will not like to have both speeds (relays) on at the same time. I had to make a circuit for Bob Kendrick that allowed him to control a Taurus fan from his GM brain that had both outputs on in high speed mode. In your case I could use a similar circuit to run the low speed fan all the time except when High speed is called for. That should allow you to run the Auto-X and then get the problem looked at.

RodneyWright · **Posted:** Tue May 12, 2015 10:58 pm

George Bright wrote:

Is that with the relay pulled out? with the relay out i would expect it to be 0v. With the relay in place I would expect it to be 12V. The PCM grounds the 86 terminal when it wants to run the fan. If you jumper the 86 terminal to ground with the relay in place it should bring on the low speed fan.

You don't want to drive around with the low speed fan jumpered on because the fan is a 2 winding motor and it will not like to have both speeds (relays) on at the same time. I had to make a circuit for Bob Kendrick that allowed him to control a Taurus fan from his GM brain that had both outputs on in high speed mode. In your case I could use a similar circuit to run the low speed fan all the time except when High speed is called for. That should allow you to run the Auto-X and then get the problem looked at.

Yes, all testing is done w/ the relay pulled out of place. If I pull the relay part way out in order to get the leads in place, I don't know if I'm making the correct contact w/ the fuse base. I'll try your test tomorrow on jumping 86 to ground w/ the relay in place.

I'm fast running out of "home repair options" for this fix. Man, I hate to know I have to take this to a dealer....

DickRasmussen · **Posted:** Wed May 13, 2015 8:16 am

RodneyWright wrote:

I'm fast running out of "home repair options" for this fix. Man, I hate to know I have to take this to a dealer....

Don't feel too bad. Reading through the service manuals for the 2012 and 2015 indicates that the diagnosis process for so many aspects of new car electronics is extremely complex and very dependent on the oem specific test equipment of similar high end equipment used by independent shops and maybe by someone like Adam of On-Site. At least if you end up paying to get this diagnosed an repaired you will know that you gave it your best effort first.

If it helps remember that it takes a lot of technology to do what modern cars do. As you know from your IT profession, complex technology is . . . complex and usually requires a lot of training, experience, and frequently specialized "tools" to troubleshoot and repair.

With this in mind I spent the $$$ for an 8 year/100K miles Ford ESP warranty on the 2015. It did help that Asheboro Ford sells those to racers at their cost.

RodneyWright · **Posted:** Wed May 13, 2015 10:33 am

George.... I pulled the high speed relay out of the way in order to have access to terminal 86 on the low speed fan. Key in the run position, engine NOT running and the low speed relay in place, I did get 12v via the multimeter, but the low speed fan did not turn on.

Going back to the initial fan wiring diagram, there's no place on there that indicates how the fan switch is supposed on interact w/ the fan. Nothing shows a link to the switch. Is the fan switch connected to the PCM and from there it triggers the low speed fan?

DickRasmussen · **Posted:** Wed May 13, 2015 2:03 pm

RodneyWright wrote:

George.... I pulled the high speed relay out of the way in order to have access to terminal 86 on the low speed fan. Key in the run position, engine NOT running and the low speed relay in place, I did get 12v via the multimeter, but the low speed fan did not turn on.

Going back to the initial fan wiring diagram, there's no place on there that indicates how the fan switch is supposed on interact w/ the fan. Nothing shows a link to the switch. Is the fan switch connected to the PCM and from there it triggers the low speed fan?

Based on the 2012 and the wiring diagram for your car I would say that the "fan switch" communicates with the PCM which then decides what to do about it.

Ditto for per the manual for our 1997 4.6L GT. Temp sensor informs the PCM which then tells the fan control system what to do.

RodneyWright · **Posted:** Wed May 13, 2015 2:58 pm

DickRasmussen wrote:

Based on the 2012 and the wiring diagram for your car I would say that the "fan switch" communicates with the PCM which then decides what to do about it.

Ditto for per the manual for our 1997 4.6L GT. Temp sensor informs the PCM which then tells the fan control system what to do.

Agreed. Took the mustang over to Dave Davis and had him hook the car up to his computer and he also looked at AllData. So, here's what we did.

> hard ground of terminal 85 w/ the relay in place caused the low speed fan to turn on, just as George said it would.
> ran a self check of the cooling system. I think most of that worked, but the fan only came on once.

From there we found the pin out on the PCM. So I need to check the continuity of the following...

> pin 7 to 85 of the low speed. That's the info out path for the PCM
> pin 41 back to fan switch. That's the info in path to the PCM.

If the continuity on both of those wires is good, then the only thing bad is the PCM itself and I get to spend a crap ton of money.

Chad Culbertson · **Posted:** Wed May 13, 2015 3:55 pm

Is the ECM tuned on the car or do you have a handheld tuner? If so sometimes the tuners can control when the fans come on, perhaps you could force it to attempt to turn the fan on at a cooler temp. My wifes jeep did some funky stuff once when I used a handheld tuner to adjust the TPMS settings along with adjusting the tire size to account for the aftermarket tires/wheels the dash would do some funky stuff.

My point being, I wonder if it's simply a programming issue in the ECM, if it's got a tune from a handheld on it, perhaps try returning to stock and reloading the tune or something. I did this for her jeep and it stopped doing funky stuff, it was pretty minor stuff though like displaying the odometer where it was have extra digits and crap in there, lol.

RodneyWright · **Posted:** Wed May 13, 2015 4:25 pm

Chad Culbertson wrote:

Is the ECM tuned on the car or do you have a handheld tuner? If so sometimes the tuners can control when the fans come on, perhaps you could force it to attempt to turn the fan on at a cooler temp. My wifes jeep did some funky stuff once when I used a handheld tuner to adjust the TPMS settings along with adjusting the tire size to account for the aftermarket tires/wheels the dash would do some funky stuff.

My point being, I wonder if it's simply a programming issue in the ECM, if it's got a tune from a handheld on it, perhaps try returning to stock and reloading the tune or something. I did this for her jeep and it stopped doing funky stuff, it was pretty minor stuff though like displaying the odometer where it was have extra digits and crap in there, lol.

Running the stock tune that came w/ the car, so nothing related to an after market tune....

RodneyWright · **Posted:** Wed May 13, 2015 5:08 pm

Well, bad news I guess. The wire continuity checks out ok, both the input and output wires are good. I think this leaves only 1 culprit to address, the PCM. Now the crying time begins....

George.... Dave Davis is pretty confident my issue is the PCM not sending out the signal to the low speed relay. Based on all the testing I've posted up here, would you concur it's the PCM? The price isn't as bad as I thought, ~600 for a new PCM, I was expecting much worse. I'm getting a price break being part of the mustang club. If you think the PCM is the issue then I'll order one. I can take this over to the ford service dept, but it's an additional 125 for diagnostics. I'd rather not spend that money if I don't have to.

Michael Westerfield · **Posted:** Wed May 13, 2015 7:26 pm

RodneyWright wrote:

> ran a self check of the cooling system. I think most of that worked, but the fan only came on once.

How mant times was it supposed to come on?

If it activated once it sounds like it is working.

George Bright · **Posted:** Wed May 13, 2015 7:52 pm

RodneyWright wrote:

Well, bad news I guess. The wire continuity checks out ok, both the input and output wires are good. I think this leaves only 1 culprit to address, the PCM. Now the crying time begins....

George.... Dave Davis is pretty confident my issue is the PCM not sending out the signal to the low speed relay. Based on all the testing I've posted up here, would you concur it's the PCM? The price isn't as bad as I thought, ~600 for a new PCM, I was expecting much worse. I'm getting a price break being part of the mustang club. If you think the PCM is the issue then I'll order one. I can take this over to the ford service dept, but it's an additional 125 for diagnostics. I'd rather not spend that money if I don't have to.

My guess is that the PCM output for the low speed fan is fried. Grounding the pin on the low speed fan verified that the relay is good. Transistors are very good at protecting fuses and relays. Or as Bob Kendrick would say "You let the magic smoke out of the PCM"

BTW The temp sensor is not a switch. It is a sensor that the PCM uses to determine coolant temp for calculations of timing, mixture, driving the temp gauge, and determining when to turn on the fans.

Richard Casto · **Posted:** Thu May 14, 2015 12:17 am

Assuming everything checks out and it points to the PCM, then that is either a hardware or software issue. Might there be something like a service bulletin that might speak to this issue? In short, is there a software update that could be applied? Along those lines, if you are considering buying a new PCM, you mentioned that you had tuning software that might be able to adjust the parameters for the fan? But you didn't want to run a non-stock tune. Is there no provision to backup the factory binary so you can revert if you want/need? And lastly, if I was to buy a new PCM, I would try to use the tuning software on the old PCM just to see what you might make it do (with respect to the fan).

Richard

Vincent Keene · **Posted:** Thu May 14, 2015 8:23 am

Not sure if Richard and I are saying the same thing or not, but since the fan can be modified via the handheld tuner, have you tried that? The PO changed the setting on my car to have the low-speed fan come on sooner than factory so I know it can be done.

Jordan Normark · **Posted:** Thu May 14, 2015 9:14 am

Vincent Keene wrote:

Not sure if Richard and I are saying the same thing or not, but since the fan can be modified via the handheld tuner, have you tried that? The PO changed the setting on my car to have the low-speed fan come on sooner than factory so I know it can be done.

I think this is what Chad was getting at also. Regardless of what you have, modified or stock tune, it makes more sense to try this before spending $600 on a new PCM you can't return.

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