Skip the auto shop - Our mechanics make house calls

Q: Speedometer stops on 40 mph until driving for 20 minutes and then regains correct speed on the speedometer with no other noticeable issues.

asked by on

replaced speedo cluster and problem is identical with replacement. local repair shop used computer to diagnose and recommended replcaing cluster. The problem does not come back until cold start. and goes away again after about 20 minutes of driving over 40. Should I replace trans speed sensor? No shifting problems or any other noted problems.
This is a class c motor home. It recently has had new brakes

My car has 72500 miles.
My car has an automatic transmission.

A: Hi there. The issue with your speedometer ...

Hi there. The issue with your speedometer not working properly is the transmission output shaft speed sensor has a faulty pickup or broken wire inside it. The speed sensor has a magnet that reads between teeth on a gear within the tail shaft of the transmission. If the magnet has metal on it from the transmission, then the magnet will become weak and not work right. Remove the speed sensor from the tail shaft of the transmission and clean it then put it back in. See if the problem continues. If the problem continues, then I recommend replacing the speed sensor. If you need further assistance troubleshooting your vehicle, then seek out a technician, such as one from Your Mechanic, that can assist you with your speedometer reading up to 40 mph, then after 20 minutes it goes up to the normal speed.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Save up to 30%

Get a quote

What others are asking

Q: Shifter lever flapping in the breeze

The shift tube in the steering column most likely broke. The shift tube is made of a weak pot metal and can break in the column. Here is a link to a picture of a broken tube in the steering...

Q: Replacing standard with automatic transmission on a VW Golf3

If you have a manual transmission, you don't want to switch it to an automatic transmission. It is too much work. Wiring harnesses would have to be changed and the computer would have to be changed. You don't really want...

Q: Break problems

Hi there: Your boyfriend has a serious brake issue that should be repaired immediately. The loud noise is most likely coming from the brake pads grinding on the brake rotors. When he applies the parking brake, it's only applying pressure...

Related articles

How Long Does a Distributor O Ring Last?
The distributor is part of the ignition system in your vehicle and its purpose is to route high voltage from the ignition coil to the spark plug. The spark plug then...
P0240 OBD-II Trouble Code: Turbocharger Boost Sensor B Circuit Range/Performance
P0240 code definition Turbocharger Boost Sensor B Circuit Range/Performance What the P0240 code means P0240 is an OBD-II generic code triggered when the Engine Control Module (ECM) detects the intake boost...
How to Avoid Back Pain in a Car
If you have back problems, sitting in a car for an extended period of time can be excruciating. Even without back problems, you could experience discomfort and soreness from...