Mechanics

TACHOMETER & SPEEDOMETER

1989 Mercedes Benz 300se

Electrical problem
1989 Mercedes Benz 300se 6 cyl Two Wheel Drive Automatic 185000 miles

About a year ago my tachometer quit working after the engine was revved while driving and the transmission shifted abruptly.

A few months ago my speedometer quit working too. I have the web driven Mercedes Service manual from MB but I have been unable to find any information in the manual on how to trouble shoot or fix either problem.
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Bryan321
February 26, 2009.




If it was me I'll start with the speedometer impulse transmitter on left rear of transmission.

Tiny
Rasmataz
Feb 26, 2009.
What about the Tach? I saw on a parts website that there are speed sensors on the front wheels. Are these for the ABS system? Not the speedometer.

Tiny
Bryan321
Feb 26, 2009.
Does it have a vehicle speed sensor I've looked couldn't find one-check that if it has one.

The ABS rpm sensor is at the front and back of the vehicle and also it has its on computer

Tiny
Rasmataz
Feb 26, 2009.
Just got off the phone w MB dealership. He could not find the speedometer impulse transmitter as a stand alone part. He mentioned a transmission harness. He also mentioned that the tachometer runs off of an engine componant, cam, crank, alternator. Do you have any ideas what runs the tachometer?
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Tiny
Bryan321
Feb 26, 2009.
The CPS gives the computer the piston postions and engine speed, CMH synchronizes the injectors and what stroke its in

Tiny
Rasmataz
Feb 26, 2009.
What is CPS & CHM?

Tiny
Bryan321
Feb 26, 2009.
CPS --Crankshaft Position Sensor

CMH--Camshaft Position Sensor

Tiny
Rasmataz
Feb 26, 2009.

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