Pcu?

[Bobgen]

I have a 04 towncar and it wont shift up . takes off in 1st and thats it. I pulled codes and now it shows random misfire. Tps switch. No trans codes. Cleared computer cleaned harness going to transmission. And car shifted fine. Next day will not shift again. Now more unrelated codes. So im thinking pcu. Does the pcu control shifting? Any thoughts would be appreciated.

 

[CuttingToolGuy]

It sounds like your PCM is going into "Limp Mode".

What Is the Ford Limp Mode?

A wide variety of Ford vehicles come with a program, controlled by the vehicle's computer, whose function is to reduce the vehicle to minimal performance standards, in the case of a vehicle component being at risk of failure. This program's informal name is a "limp mode."

itstillruns.com

In short, the computer thinks something is wrong and won't let you go fast to keep from making things worse.

 

[Bobgen]

It sounds like your PCM is going into "Limp Mode".

What Is the Ford Limp Mode?

A wide variety of Ford vehicles come with a program, controlled by the vehicle's computer, whose function is to reduce the vehicle to minimal performance standards, in the case of a vehicle component being at risk of failure. This program's informal name is a "limp mode."

itstillruns.com

In short, the computer thinks something is wrong and won't let you go fast to keep from making things worse.

It will not go into any upper gears above 1st. And the random eng. Codes leed me to believe its the pcu. If its in limp mode it would go into upper gears right? Motor runs perfect.

 

[04TC]

It will not go into any upper gears above 1st. And the random eng. Codes leed me to believe its the pcu. If its in limp mode it would go into upper gears right? Motor runs perfect.

When you manually shift into "2" shift lever position while driving, does it shift into 2nd gear?

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[Bobgen]

When you manually shift into "2" shift lever position while driving, does it shift into 2nd gear?

No nothing i do will help. I cleaned the wiring harness going to transmission and it worked for a while but after i shut it off it would not shift again. When it works it shifts perfect. That means the transmission is ok right? Im thinking its either the pcu or the shift solenoid.

 

[04TC]

No nothing i do will help. I cleaned the wiring harness going to transmission and it worked for a while but after i shut it off it would not shift again. When it works it shifts perfect. That means the transmission is ok right? Im thinking its either the pcu or the shift solenoid.

I wouldn't rule it out completely that the transmission has a problem. When we had a Plymouth minivan the transmission started to go out, sometimes it would not shift out of first and sometimes only stayed in 1st, 2nd, (or reverse). Later it wouldn't shift out of first unless we manually moved the shifter and eventually it only had 1st and reverse. We kept driving it around town in 1st gear 30mph and that eventually caused the engine to blow up. But my experience is just an anecdote, you could easily be right that it is the PCM or a solenoid. It seems likely. I don't know what else would cause the problem you are describing.

 

[Bobgen]

I wouldn't rule it out completely that the transmission has a problem. When we had a Plymouth minivan the transmission started to go out, sometimes it would not shift out of first and sometimes only stayed in 1st, 2nd, (or reverse). Later it wouldn't shift out of first unless we manually moved the shifter and eventually it only had 1st and reverse. We kept driving it around town in 1st gear 30mph and that eventually caused the engine to blow up. But my experience is just an anecdote, you could easily be right that it is the PCM or a solenoid. It seems likely. I don't know what else would cause the problem you are describing.

Thanks to everyone.... I will post my findings when repairs are complete. In case someone else has a similar issue.

 

[Bobgen]

Thanks to everyone.... I will post my findings when repairs are complete. In case someone else has a similar issue.

Update .... I did a hard reboot of computer and car shifts like a new car. We shall see if it continues.

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[Bobgen]

Update .... I did a hard reboot of computer and car shifts like a new car. We shall see if it continues.

Nope its acting up again

 

[CuttingToolGuy]

In the first post you mentioned you had engine trouble codes. What numbers are they?

Do you have an ADL interface that can read the PIDs live?

 

[Bobgen]

In the first post you mentioned you had engine trouble codes. What numbers are they?

Do you have an ADL interface that can read the PIDs live?

Its giving random misfire tps switch map sensor. And that does not make sense. The car runs fine sometimes. Until it doesn't.. Lol i cant think of anything else but the pcu. But a lot of people are telling me the pcu hardly ever goes out on these cars

 

[CuttingToolGuy]

I am not familiar with the 03+ wiring schematics but, I am suspicious if all the related components that are showing errors have a common ground or power supply.

I have also heard of a symptom of alternators going bad and creating frequencies that interfere with sensor / PCU communication.

At any rate, I think you need to find a technician with a Snapon type scanner and see what they can see from all these errors. A Ford scanner will also work. Some people have used a laptop with a program called "Forscan", I have never used it and can't vouch for it.

I believe if you fix these errors you will get your transmission back.

I agree that it is rare for the PCU to fail and even if you plan to swap one out you will have to go through a procedure with a Snapon, Ford or Forscan to successfully do so.

______________________________

 

[Bobgen]

I am not familiar with the 03+ wiring schematics but, I am suspicious if all the related components that are showing errors have a common ground or power supply.

I have also heard of a symptom of alternators going bad and creating frequencies that interfere with sensor / PCU communication.

At any rate, I think you need to find a technician with a Snapon type scanner and see what they can see from all these errors. A Ford scanner will also work. Some people have used a laptop with a program called "Forscan", I have never used it and can't vouch for it.

I believe if you fix these errors you will get your transmission back.

I agree that it is rare for the PCU to fail and even if you plan to swap one out you will have to go through a procedure with a Snapon, Ford or Forscan to successfully do so.

Thanks so much for your advice. Thats exactly what im going to do. I was thinking about the same.

 

[Brian J. Patterson]

Its giving random misfire tps switch map sensor. And that does not make sense. The car runs fine sometimes. Until it doesn't.. Lol i cant think of anything else but the pcu. But a lot of people are telling me the pcu hardly ever goes out on these cars

Hi, Bobgen.

I would also test the Throttle Position Sensor (TPS) and Mass-Airflow Sensor (MAF sensor, which you called the "map sensor,") since both are sending fault codes.

Transmission shifting is governed in part by the throttle position. If the TPS is sending erroneous information downstream, having the car go into "limp mode" is just one possibility.

The MAF sensor, which measures the air being drawn into the engine, can force the car into "limp mode" if failing, depending on how exactly it's going bad. If it quits completely, the car won't run or start.

Good luck.

 

[Bobgen]

Hi, Bobgen.

I would also test the Throttle Position Sensor (TPS) and Mass-Airflow Sensor (MAF sensor, which you called the "map sensor,") since both are sending fault codes.

Transmission shifting is governed in part by the throttle position. If the TPS is sending erroneous information downstream, having the car go into "limp mode" is just one possibility.

The MAF sensor, which measures the air being drawn into the engine, can force the car into "limp mode" if failing, depending on how exactly it's going bad. If it quits completely, the car won't run or start.

Good luck.

Tks i will check it

 

[Bobgen]

Tks i will check it

Update........ I had a oil leak that spread oil in the wiring harness. That was causing the codes. Looks like just cleaning the harness well is going to fix this now that the oil leak is fixed.

______________________________

 

[Bobgen]

I have a 04 towncar and it wont shift up . takes off in 1st and thats it. I pulled codes and now it shows random misfire. Tps switch. No trans codes. Cleared computer cleaned harness going to transmission. And car shifted fine. Next day will not shift again. Now more unrelated codes. So im thinking pcu. Does the pcu control shifting? Any thoughts would be appreciated.

Update: found out it was just a faulty tps switch that caused the issue. Car shifts perfect now.

 

[Bobgen]

I am not familiar with the 03+ wiring schematics but, I am suspicious if all the related components that are showing errors have a common ground or power supply.

I have also heard of a symptom of alternators going bad and creating frequencies that interfere with sensor / PCU communication.

At any rate, I think you need to find a technician with a Snapon type scanner and see what they can see from all these errors. A Ford scanner will also work. Some people have used a laptop with a program called "Forscan", I have never used it and can't vouch for it.

I believe if you fix these errors you will get your transmission back.

I agree that it is rare for the PCU to fail and even if you plan to swap one out you will have to go through a procedure with a Snapon, Ford or Forscan to successfully do so.

By the way i did check the voltage and the alternator was putting out too much voltage and that could have caused the tps switch and the other 2 issues so i installed a new alternator after replacing the 3 items and now the car is doing great.

 

[CuttingToolGuy]

Good to hear.

And thanks for reporting back. It is so frustrating when searching for a solution to a problem one has and the thread just dies without a conclusion. You have probably just helped someone in 2025!

 

[Bobgen]

Cool i can affect the future..... Wish i could predict the covid stuff or election....... Lol