New PCM forced idle

[navybonehead]

I installed a rebuilt PCM from flagship one this weekend, not the truck only starts in forced idle mode.
It had been dying occasionally while driving, or just not starting. DTCs led me to believe it was the throttle body so I replaced that new. Problem continued, so I also replaced the TPS sensor harness. Problem recently got worse to where it would seldom start, so I had my local dealer check it; they said there were multiple DTCs from PCM malfunction and it would need to be replaced and checked again. So in went the new PCM, and a locksmith came and did the key relearn procedure, and it started. But it has not been driven yet because of forced (and very rough) idle, and gas pedal does nothing.
Help please!

 

[Zorin]

To start, you will want to get a copy of Forscan on a laptop, and a OBD adapter.

A problem like this, you NEED to pull DTC's, and you NEED to see live data.

What were the DTC's they found that supported the need for a PCM? I rarely replace them, it's usually a bad sensor or some bad wiring causing the problem.

Tim

 

[navybonehead]

To start, you will want to get a copy of Forscan on a laptop, and a OBD adapter.

A problem like this, you NEED to pull DTC's, and you NEED to see live data.

What were the DTC's they found that supported the need for a PCM? I rarely replace them, it's usually a bad sensor or some bad wiring causing the problem.

Tim

Thanks for the reply. I need to find the sheet with the codes it had previously. Right now when I start it I get P2104, P2107, P2110. I have a scanner which does live data and other functions, though it is not bidirectional.

 

[Zorin]

Thanks for the reply. I need to find the sheet with the codes it had previously. Right now when I start it I get P2104, P2107, P2110. I have a scanner which does live data and other functions, though it is not bidirectional.

I don't think bi directional is terribly important right now, but the ability to see live data is pretty key.

Is your Explorer a V6 or a V8?

Tim

 

[Zorin]

Also, scope this out.

Look down INSIDE that wire loom for faults in the wiring.



Tim

 

[navybonehead]

Thanks for the reply. I need to find the sheet with the codes it had previously. Right now when I start it I get P2104, P2107, P2110. I have a scanner which does live data and other functions, though it is not bidirectional.

I don't think bi directional is terribly important right now, but the ability to see live data is pretty key.

Is your Explorer a V6 or a V8?

Tim

It’s a v6. I uploaded a shot from the dealer report which has the codes pulled when the PCM was malfunctioning.

 

[Zorin]

Very interesting.....P1635 and U0300 - these point to tire size reprogramming issues. Not that we care about that, it won't cause this.

P0607 indicates an internal malfunction in the PCM, most likely corrupted RAM that could stem from improper reprogramming issues. P060B usually indicates a failed PCM.

Most of other codes point to the electronic throttle control, except the P061D, that one indicates that there's a Mass Air Sensor concern. However, if the engine dies and sputters or stalls, it COULD set as a result of that instead of an actual hardware fault.

I'm sticking with bad wiring further down the way from the electronic throttle control unit. I know you had the pigtail replaced, but how far down into the harness did they go?

Now, it's worth mentioning that I have known some folks to get a bad PCM from Flagship One, and by and large, the reman PCMs from places like that can be sketchy. But let's not explore that until we make certain that the wiring is intact. One way to do that is to key up your live data on a lot of the throttle parameters, then go shake the harness under the hood. Watch the data. It should not change as you do this. If it jumps around or you get freaky readings, then you know where to start narrowing it down to search for compromised wiring.

Tim

 

[navybonehead]

Very interesting.....P1635 and U0300 - these point to tire size reprogramming issues. Not that we care about that, it won't cause this.

P0607 indicates an internal malfunction in the PCM, most likely corrupted RAM that could stem from improper reprogramming issues. P060B usually indicates a failed PCM.

Most of other codes point to the electronic throttle control, except the P061D, that one indicates that there's a Mass Air Sensor concern. However, if the engine dies and sputters or stalls, it COULD set as a result of that instead of an actual hardware fault.

I'm sticking with bad wiring further down the way from the electronic throttle control unit. I know you had the pigtail replaced, but how far down into the harness did they go?

Now, it's worth mentioning that I have known some folks to get a bad PCM from Flagship One, and by and large, the reman PCMs from places like that can be sketchy. But let's not explore that until we make certain that the wiring is intact. One way to do that is to key up your live data on a lot of the throttle parameters, then go shake the harness under the hood. Watch the data. It should not change as you do this. If it jumps around or you get freaky readings, then you know where to start narrowing it down to search for compromised wiring.

Tim

Thanks for the insight. The wheels/tires were aftermarket when I bought it several years ago, but I recently changed to a factory set which do not have TPS in them.
As for the pigtail, I only replaced the connector and about 12” of pigtail.
I’ll do the check on the harness as suggested, I’m using an app that connects to the scanner to read live data. So far it never registers any throttle input when pressing the pedal.

 

[Zorin]

Thanks for the insight. The wheels/tires were aftermarket when I bought it several years ago, but I recently changed to a factory set which do not have TPS in them.
As for the pigtail, I only replaced the connector and about 12” of pigtail.
I’ll do the check on the harness as suggested, I’m using an app that connects to the scanner to read live data. So far it never registers any throttle input when pressing the pedal.

No register when you press the accelerator....big clue!

Next time you hook up to it, make sure to key on your accelerator pedal position sensors as well. This way, you can see if the PCM is seeing an input from the accelerator pedal, and this will rule out the accelerator pedal assembly. You may have to clear the codes to get it to re-enable, but all you need is for a split second to see the gas pedal moving. If your tool supports it, see if you can see desired throttle angle and compare it to actual. If you can see movement on the APP sensors, and a desired throttle reading, then you know the APP sensors are working, AND that the PCM has control. At that point you are really looking at wiring.

Tim

 

[navybonehead]

No register when you press the accelerator....big clue!

Next time you hook up to it, make sure to key on your accelerator pedal position sensors as well. This way, you can see if the PCM is seeing an input from the accelerator pedal, and this will rule out the accelerator pedal assembly. You may have to clear the codes to get it to re-enable, but all you need is for a split second to see the gas pedal moving. If your tool supports it, see if you can see desired throttle angle and compare it to actual. If you can see movement on the APP sensors, and a desired throttle reading, then you know the APP sensors are working, AND that the PCM has control. At that point you are really looking at wiring.

Tim

Ok I git a look at the throttle and accelerator on my scanner. “Absolute pedal position” changes in response to the pedal. Relative and absolute throttle position as well as commanded throttle position are completely static. I take it to mean that the pedal is working (as it always has before) but the PCM is keeping the engine at fixed throttle, which is why the forced idle DTC pops every time I start it.
I still need to try poking around the harness, but it has been raining too much today.

 

[Zorin]

Sure sounding like wiring. The PCM sees that you are pressing it, and when it doesn't get a response back from the throttle position sensors, it shuts everything down and goes to forced idle.

Tim

 

[navybonehead]

Sure sounding like wiring. The PCM sees that you are pressing it, and when it doesn't get a response back from the throttle position sensors, it shuts everything down and goes to forced idle.

Tim

Is that the reason I am always gettin the codes for throttle actuator control? I mean it makes sense, it’s just that I don’t understand why it had been driving fine most of the time on the original PCM, including the day I swapped in the new one. Could the original one have been ignoring the TPS?
Also, shaking the harness around didn’t show anything on the scanner. Is it possible to read voltages at the connectors with a multimeter to diagnose the harness?

 

[Zorin]

Yeah, pretty much, I think.

Using a multimeter to check the harness is definitely doable, however, you won't want to use voltages. As soon as you press the gas, and the PCM doesn't see a response from the throttle body, it pretty much disables throttle control entirely.

You'll need a wiring schematic, and you will want to check continuity between the throttle body connector, and the PCM connector. Basically, just put the meter on beep function, and then see if you get a beep from each end of the wire. The one that doesn't beep tells you that wire is not continuous (open circuited).

I highly doubt the original PCM was "ignoring" the TPS. It is somewhat possible that due to a fault in the PCM, it didn't recognize the fault that is now occurring - but that's highly speculative.

Tim

 

[navybonehead]

Yeah, pretty much, I think.

Using a multimeter to check the harness is definitely doable, however, you won't want to use voltages. As soon as you press the gas, and the PCM doesn't see a response from the throttle body, it pretty much disables throttle control entirely.

You'll need a wiring schematic, and you will want to check continuity between the throttle body connector, and the PCM connector. Basically, just put the meter on beep function, and then see if you get a beep from each end of the wire. The one that doesn't beep tells you that wire is not continuous (open circuited).

I highly doubt the original PCM was "ignoring" the TPS. It is somewhat possible that due to a fault in the PCM, it didn't recognize the fault that is now occurring - but that's highly speculative.

Tim

Thank you again. I’ll try that tonight once I find a schematic. One thing I discovered today, probably unrelated, is a broken vacuum line. It was melted in half where it contacted the egr valve housing. It’s a very thin plastic line, I believe it enters the firewall to control the AC door.
Also, I tried connecting the original pcm to see what the throttle would do, and I could see it actuate (of course it won’t start b/c of the PATS being reflashed. But with the new pcm it doesn’t budge at all when turning the key to run.

 

[Zorin]

Thank you again. I’ll try that tonight once I find a schematic. One thing I discovered today, probably unrelated, is a broken vacuum line. It was melted in half where it contacted the egr valve housing. It’s a very thin plastic line, I believe it enters the firewall to control the AC door.
Also, I tried connecting the original pcm to see what the throttle would do, and I could see it actuate (of course it won’t start b/c of the PATS being reflashed. But with the new pcm it doesn’t budge at all when turning the key to run.

Hmmmm.


That's why I'm harping on checking wiring. You want to be sure the car is OK before calling another bad PCM.

Interesting tidbit, my other car is a 2002 Ford Mustang GT. It blew its engine computer as well. Headed down to the local parts store, bought one, came preflashed, I programmed the keys, and it ran for about 30 days. Then it quit. Checked everything, called a PCM, warrantied it, same exact thing happened TWO more times. 30 days, dead PCM.

They swore it was my car. I told them I would prove it was not. I went and bought the absolute cheapest used OEM PCM I could find on eBay, had it flashed, I programmed the keys, and the car has run flawless for about 6 months now.

You may want to invest in a OBD Link MX, and get Forscan on a laptop. That way, you can program the keys and do parameter resets yourself instead of paying someone to come in and do it.

My long winded point - diagnose your car, check your wiring. If you are in good shape, then you know to call a bad PCM. The fact that the throttle wants to come to life with the old PCM is somewhat telling, but use that as a little clue while you double check.

Tim

 

[navybonehead]

Hmmmm.


That's why I'm harping on checking wiring. You want to be sure the car is OK before calling another bad PCM.

Interesting tidbit, my other car is a 2002 Ford Mustang GT. It blew its engine computer as well. Headed down to the local parts store, bought one, came preflashed, I programmed the keys, and it ran for about 30 days. Then it quit. Checked everything, called a PCM, warrantied it, same exact thing happened TWO more times. 30 days, dead PCM.

They swore it was my car. I told them I would prove it was not. I went and bought the absolute cheapest used OEM PCM I could find on eBay, had it flashed, I programmed the keys, and the car has run flawless for about 6 months now.

You may want to invest in a OBD Link MX, and get Forscan on a laptop. That way, you can program the keys and do parameter resets yourself instead of paying someone to come in and do it.

My long winded point - diagnose your car, check your wiring. If you are in good shape, then you know to call a bad PCM. The fact that the throttle wants to come to life with the old PCM is somewhat telling, but use that as a little clue while you double check.

Tim

Ok, I'm definitely considering upgrading my scanner, because the locksmith raked me over the coals. If I can identify a harness issue, and reuse my original PCM, you're saying that Forscan will allow me to reset parameters and relearn my keys? I use a bluetooth scanner with the "Car Scanner" app, but it lacks this capability.

 

[Zorin]

Ok, I'm definitely considering upgrading my scanner, because the locksmith raked me over the coals. If I can identify a harness issue, and reuse my original PCM, you're saying that Forscan will allow me to reset parameters and relearn my keys? I use a bluetooth scanner with the "Car Scanner" app, but it lacks this capability.

Yeah, Forscan is what I use on most Fords I work on.

Definitely pop the hundred bucks for the OBDLink MX dongle, it makes it work almost as well as a factory IDS setup. You will want this set up on a laptop, using the Lite version for a phone lacks a LOT of functionality.

So, here's what you will want -
Laptop with bluetooth capability
Forscan download - Free
OBDLink MX+ - $100

Tim

 

[Bazz270]

If you want this vehicle for the next years,

Youve better replace the whole engine harness before any electric diagnistics started.try to find one first.

Bad exhaust manifolds could cause high engine bay temperature that totally melting the insulation.check for exhaust manifold studs missed or deformated.


Unless the harness and the manifold stay bad,you will always get an error codes.it really never ends

 

[navybonehead]

If you want this vehicle for the next years,

Youve better replace the whole engine harness before any electric diagnistics started.try to find one first.

Bad exhaust manifolds could cause high engine bay temperature that totally melting the insulation.check for exhaust manifold studs missed or deformated.


Unless the harness and the manifold stay bad,you will always get an error codes.it really never ends

Thank you, I did some more sniffing around the harness and found some exposed wires coming from the throttle control. I taped the wires up neatly but no change.
So today I put the original PCM back in and used FORscan to relearn my keys. It started up and idled well for a few minutes. I shut it off and went inside to eat some lunch. When I got back to the car it started, sputtered and died, and now it won’t restart. The only DTC shown was P0191. I cleared that, and when attempting to start now it gives no codes.

 

[Zorin]

Thank you, I did some more sniffing around the harness and found some exposed wires coming from the throttle control. I taped the wires up neatly but no change.
So today I put the original PCM back in and used FORscan to relearn my keys. It started up and idled well for a few minutes. I shut it off and went inside to eat some lunch. When I got back to the car it started, sputtered and died, and now it won’t restart. The only DTC shown was P0191. I cleared that, and when attempting to start now it gives no codes.

OK, so P0191 is a fuel rail pressure code.

Sputtered and died. This says you aren't getting gas!

Quick and easy check. Pull the air intake hose, give it a shot of brake cleaner or starter fluid. If it cranks right up and runs, see if you can keep it alive on the sauce.

Of course, do the regular checks, see if you hear the EFI pump priming for 3 seconds when you turn the key to ON, etc.

Tim