Hi,

The ABS light is on and the speedometer does not work on my '95 Volvo 940. The error code is 155, which means "Rear axle sensor: open circuit or short-circuit to battery voltage".

What I have done:
Checked for continuity between sensor and ground - pass
Checked for continuity between sensor and ABS module for both leads - pass
Tried clearing code - still got same code next time I checked
Replaced rear axle sensor - still doesn't work and still same code.

Ideas to try next:
Replace the ABS module?

Any other ideas? What could the problem be? How could I diagnose it?

Thanks!

 

[the following is from greenbook TP5901031, ABS Troubleshooting for 1993- 940 ]

the ABS sensors should NOT be connected to ground, except inside the ABS controller (and, for the rear sensor, the speedometer)

according to the greeenbook at the connector to the ABS control unit, with the rear wheel turning, you should see about 2mV DC

if you can 'tap' pin 7 (+ sensor) and pin 9 (0/ground to sensor) of the ABS control unit, and connect a volt meter set to AC, you should see pulses of 0.5 to maybe 2V AC if you spin a rear wheel (with the ignition on)

if you disconnect the ABS computer (ignition OFF first), and connect an OHM meter between pins 7 and 9, you should see 800-1400 ohms. now unplug the speedo/abs sensor at the differential, and you should see open circuit.

the ABS sensor wiring goes through connectors C1 (53 pin instrument panel harness at door sill) and C155 (connector left A-post, 8 pin). brown-white is the ground side (again, grounded only at the ABS controllerr and the speedometer, NOT at the sensor!) and goes through C1 pin 11 and C155 pin 5, then on to ABS controller pin 9. green-white is the signal from the sensor and goes through C1 pin 12 and C155 pin 6 then on to the ABS controller pin 7.

the speedo is connected via C1, not C155.

I hope this is of some help?

 

I'd also make sure the alternator is not overcharging as that would cause the ABS light to come on.

 

wouldn't that have a different ABS fault code than the rather specific 1-5-5 which says the rear sensor is open or shorted to + (not ground). I suppose the short also could be in the speedometer, as that is wired to the same rear sensor.