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Ask sprinkles08 Your Own Question
sprinkles08, ASE Certified Technician
Category: Chrysler
Satisfied Customers: 23004
Experience:  ASE Master & Advanced level certified, Chrysler Master Certified, Trans and Hybrid Specialist
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Speedometer jumping while in park. just had a P0128 code on

Customer Question

JA: Hi. How can we help?
Customer: speedometer jumping while in park. just had a P0128 code on and check engine light on. turn ac on while in park and revs up to 20mph
JA: Does the light stay on, or does it blink?
Customer: check engine light stays on
JA: What is the model/year of your Chrysler?
Customer: 2005 chrysler sebring touring convertible
JA: Are you fixing your Sebring yourself? What have you tried so far?
Customer: nothing but computer checks and if its a easy fix i will yes fix it myself
JA: Anything else you want the mechanic to know before I connect you?
Customer: no
Submitted: 11 months ago.
Category: Chrysler
Expert:  Cary York replied 11 months ago.

Hi, I’m Cary and I’ll be helping you today.
Please understand that I can't smell, hear, or touch the vehicle, so patience is appreciated. Before leaving the site make sure and leave me a rating. You can still reply to me as many times as needed, even after the rating..

Did the check engine light and speedo problem all start at the same time?

Customer: replied 11 months ago.
no the spedo problem first then two days later the check engine light
Expert:  Cary York replied 11 months ago.

Lets address the engine light first. Is the coolant full and/or does it run hot?

Customer: replied 11 months ago.
coolant is full and the engine runs fine. no overheating.. a little over a year ago i had the water pump, all hoses and thermostat and cooling sensor replaced brand new.
Expert:  Cary York replied 11 months ago.

The code P0128 is referring to the coolant sensor. I would diag that first. Then the speedo. Let me look at something and I'll be right back.

Customer: replied 11 months ago.
Expert:  Cary York replied 11 months ago.

Is this an auto or man trans?

Customer: replied 11 months ago.
Expert:  Cary York replied 11 months ago.

Is that the only code and have you tried to clear and see if it returns?

Customer: replied 11 months ago.
that is the only code that has come up.. and no i dont know how to clear it sorry
Expert:  Cary York replied 11 months ago.

Is the speedo problem consistent or intermittent?

Customer: replied 11 months ago.
its fine as long as i dont have the a/c running.. if the a/c is off and i am driving then it doesnt do that .. if i turn the a/c on then it does it. if the a/c is on and i shift to reverse it shifts hard. if the ac is off it runs and drives like new
Expert:  Cary York replied 11 months ago.

Do you know if the radiator cooling fans are working or not?

Customer: replied 11 months ago.
they are working fine
Expert:  Cary York replied 11 months ago.

This sounds like a possible ground circuit problem. Unfortunately it sounds to be a hands on diag problem. I will opt out to see if another expert can help.

Customer: replied 11 months ago.
no i cant afford to have any more debited from my account
Expert:  sprinkles08 replied 11 months ago.

Hello and welcome to JustAnswer!

If the coolant is full then the thermostat will need to be replaced to repair the P0128. A Mopar thermostat needs to be used as aftermarkets have shown poor quality.

The speedometer issue is being caused by electrical noise from a failing alternator. Unplug the alternator field connector and you'll see the speedometer drop back to zero. If so then replace the alternator.