2010 Chrysler 300 Speedometer not working

Tiny
HEATHERMARIE29
  • MEMBER
  • 2010 CHRYSLER 300
  • 2.5L
  • 4 CYL
  • TURBO
  • RWD
  • AUTOMATIC
  • 80,000 MILES
All of a sudden, the speedometer stopped registering the speed of travel. At the same time the cruise control won't work, the automatic heating/cooling won't work, and the Brake light in the dash along with the ABS light are on. Occasionally the Brake light will go out, and the speedo will start registering rate of travel, but this only lasts for a short time. We have checked the fuses and replaced one that was blown, but the rest appear to be intact. We suspect perhaps that a relay is on its way out, but our owners manual is rather vague about what certain fuses are for or which relays control which functions.
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Tuesday, June 16th, 2015 AT 6:21 PM

3 Replies

Tiny
CARADIODOC
  • EXPERT
You have an intermittent problem. Fuses are never intermittent. When they blow, they're done, and that circuit will never work again until it is replaced. There's no relay's involved with the speedometer. Relays are used to power up high-current circuits. The most likely suspect for an intermittent speedometer is a failing speed sensor on the transmission. The cruise control system needs that information too, and that would explain why that stops working at the same time, but it's hard to know if or how the other symptoms figure in. On a lot of newer cars we're running into things that stop working due to causes that are seemingly totally unrelated. I would concentrate on the speedometer first, then see if the heater problem is still there.

The place to start is by reading the diagnostic fault codes. Chrysler makes doing that yourself very easy. Cycle the ignition switch from "off" to "run" three times within five seconds without cranking the engine, leave it in "run", then watch the code numbers appear in the odometer display. Reply back with those numbers, then I'll see if they could be related to this problem.
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Tuesday, June 16th, 2015 AT 6:56 PM
Tiny
HEATHERMARIE29
  • MEMBER
Thanks for getting back to me. I did the diagnostic code test and it came back with the following codes.
0121
1110
1120
0121
done
I look forward to hearing from you.
Heather
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Wednesday, June 17th, 2015 AT 7:26 AM
Tiny
CARADIODOC
  • EXPERT
P0121 - Throttle/Pedal Position Sensor/Switch A Circuit Range/Performance Problem
P1110 - Atmospheric Pressure Sensor Low Input
P1120 - TPS Out Of Range Low

At first glance, none of these have anything to do with the speedometer. We've been running into a lot of weird symptoms though that seem to have nothing in common with their causes. A friend recently ran into a truck that had a very noisy transmission, and that cleared up after repairing a broken wire for the ambient air temperature sensor. That one really surprised us, but we've been seeing more and more things like that the last few years.

You didn't list the right engine size so I'm not sure which throttle system you have, but if it's the "throttle-by-wire" system which adds another unreliable computer to the car, I can see where these things can all be related. There's two things to consider. First, have the dealer erase the fault codes, then test the electronic throttle system. If that solves the problem, at least for now, they may be using the speedometer as a way of getting your attention so you have the throttle system repaired. In my opinion, electronic throttle systems are dangerous and I'll never own a car with one. That's what put Toyota in the news a few years ago.

The second thing the mechanic can do is use the scanner to view live data to see why the cruise control won't set, and its "reason for last cutout". I suspect the "reason" will be "vehicle speed too low" or "below minimum threshold", but that will just verify what we already know about the missing speed signal. From there, he can see if multiple computers aren't getting the speed signal, or if just one computer isn't reading the signal being sent to it.
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Thursday, June 18th, 2015 AT 7:18 PM

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