Does a catalytic converter affect the speedometer?


Hi I drive a 92’ dodge caravan, I know it’s old with approx. 170,000 miles on it. It has a 3.3 engine and front wheel drive. I’ve been having problems with the speedometer going crazy, not allowing me to go over 45 mph without the speedometer jumping to 100mph to 0, and sometimes causing the car to cut out and jerk. this has been going on for months and gotten worse. I’ve taken it to the mechanics and had sensors changed, it didn’t work. they didn’t know what was wrong with it. well I was driving my vehicle when all of a sudden it got really loud and wouldn’t get any speed. I pulled over, it was embarrassingly loud, and crawled under the vehicle to check out the muffler sense I had just had it replaced. nothing was wrong with it that I could see utill I looked further under the vehicle and saw it had become disconnected at the catalytic converter. I took the car and had it repaired and so far, knock on wood, the speedometer hasn’t gone crazy at all. Does anyone know if the C.C. maybe sucking in air, could affect the speedometer or has anyone ever had this problem? Thanks for responses


No connection.


The speedometer has no connection whatsoever to the catalytic converter.


No again. But we still cannot account for your car’s behavior.


[b]No. The cat doesn’t effect the speedometer function. But the Vehicle Speed Sensor does.



The speedometer problem may be the body conrol module starting to go, which is completely unrelated to the cat.

Eventually, if it gets bad enough, the windshield wipers will also randomly turn on and the dash lights will start to do funny things.

The BCM is about $300.00, so wait until it gets really bad before you change it.


I don’t know how the vehicle is configured, but if that pre-cat joint that came disconnected was blowing hot exhaust gas onto the output leads for the vehicle speed sensor it could affect the signal to the speedo/odometer. It could cause harness damage that could cause an intermittant loss of signal.

The other possibility is that when the mechanic fixed the cat converter leak he simply fixed a wire coming from the VSS that he noticed broken without mentioning it.

  • mountainbike