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Limp Mode and speedo -same time

 
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Old 10 Feb 2018, 02:28 pm
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Default Limp Mode and speedo -same time

2005 Turbo with on going off again and on again problem.

After driving awhile upon typical slow down/downshifting car goes into limp mode and speedo bounces from 0 to 40-50-60 MPH. I remedy by pulling over,
turning ignition from accessory to instrument lights on 3-4 times and driving off with normal transmission operation.

During a 3- 40 mile drive this may be needed 2-4 times then won't reoccur
for a week or two...seems to have a pattern.

I need to resolve this problem. Current codes are o720 and 0700.

Hate to go to transmission shop...$$$$

Help, Paul
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Old 10 Feb 2018, 04:01 pm
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Join Date: Aug 2014
Location: Thousand Oaks, CA
Posts: 7,333
Default Re: Limp Mode and speedo -same time

Quote:
Originally Posted by paulwells77 View Post
2005 Turbo with on going off again and on again problem.

After driving awhile upon typical slow down/downshifting car goes into limp mode and speedo bounces from 0 to 40-50-60 MPH. I remedy by pulling over,
turning ignition from accessory to instrument lights on 3-4 times and driving off with normal transmission operation.

During a 3- 40 mile drive this may be needed 2-4 times then won't reoccur
for a week or two...seems to have a pattern.

I need to resolve this problem. Current codes are o720 and 0700.

Hate to go to transmission shop...$$$$

Help, Paul
I would suggest checking the wiring going to the output speed sensor and the output speed sensor itself.
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Old 10 Feb 2018, 04:07 pm
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Location: Arkansas
Posts: 10,412
Default Re: Limp Mode and speedo -same time

You may be really lucky here. The P0720 is Output Speed Sensor Circuit Malfunction. A intermittently bad speed sensor would give exactly the symptoms you have and may set off the generic P0700 as well. This sensor is located on the transmission almost directly below the battery.

The speed output sensor is fairly easy to reach and change out. Other things that may cause this is damaged wiring or loose plug on the sensor, an ignition switch fault, or a number of less likely things as well.

If me, I'd start by inspecting the wiring to the speed sensor. I'd remove the plug, clean it with electrical cleaner and put it back on. Then I'd clear the trouble codes with my code reader and drive the car to see if the problems return. If so, I'd likely change out the sensor. They are fairly inexpensive. There's no guarantee this is the problem. But it's the most likely and easy to try.

Amazon has the input and output speed sensors in a pair for around $15

https://www.amazon.com/Transmission-...+output+sensor

My choice would be this Dorman sensor for $12.08 plus free Prime shipping:

https://www.amazon.com/dp/B0048YKWO8...1188--1-0&sr=1

The Mopar sensor is around $28

https://www.amazon.com/Mopar-4800879...+output+sensor

Be sure to look up the correct part number for you car before you buy. RockAuto has a much better and more accurate application guide. I often look up the part number there and then buy from Amazon where I get free and faster shipping. Most brick and mortar parts stores will have this sensor as well. It fits many different Mopar vehicles from the PT era.

PS: If you need a copy of the service manual for your car, you can download it from my Google Drive at this link:

https://drive.google.com/file/d/0B9C...ew?usp=sharing
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Old 10 Feb 2018, 04:48 pm
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Join Date: Jun 2014
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Default Re: Limp Mode and speedo -same time

It looks like you have been fighting this problem for more than 2 years now!

Speedometer/Odometer/trans. jerky

It looks like you have already changed the output sensor at least once, so it may not be that.

In another one of your threads you mentioned the red light in the dash coming on intermittently. Is it still doing that? If so, it is very possible that your PCM is failing. Usually when that light comes on when you are driving, then that's the cause and could also explain the codes and actions you are describing now.

These PTs are very susceptible to power fluctuations due to bad grounds and possibly even the alternator. I was reading on another forum where the owner of a Chrysler Pacifica had both 0700 and 0720. He replaced the output sensor but after a while the problem came back. In the end he narrowed it down to a bad alternator giving a dirty signal due to what he described as a failed diode. He replaced the alternator and the problem disappeared and never came back.

I am not suggesting that is what your problem is, but you should check everything. All grounds and all power connections.
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