ABS light
 

Hello, the abs light is on on my 1994 XJ81 and my speedometer doesn't work. I have checked the fuses and they are good. I think the signal for the speedo comes from the front passenger side speed sensor? Can I check it with an ohmmeter ? How should I proceed? Best Regards

Hi jagnut,

I can never keep it straight as to which wheel speed sensor provides the vehicle speed signal via the ABS module to the IC, because it varies between the different Jaguar models, but there is some diagnostic information beginning on pdf page 116 of the manual at this link:

AJ6 4.0L Engine Management System / OBDI Diagnostic Guide

You can also measure the DC resistance across the connector terminals of each wheel speed sensor to see if one sensor is significantly different than the others. While you are measuring the resistance, manipulate the wiring harness along its length to test for a break in a wire. It is also worth cleaning the sensors and reluctor wheels / tone rings since brake dust and rust buildup can interfere with proper operation.

Cheers,

Don

I think you will find the speed sensor is off a reluctor wheel on the half shaft.

Hello again, checked the resistance value for frt. right sensor around 1100 ohms same as left frt sensor. pulled and cleaned sensor and blew compressed air to clean reluctor. looked for damaged teeth. Looked good. I did notice that the securing bolt has a added ground wire attached. It is secured on the other end to the metal bracket that secures the brake hose. On the other front sensor this ground wire has broken in half. Perhaps this is the fault. I will replace this weekend.Is this a factory installation? The ground cables are encased in a rubber insulator and are of the braided wire type. Thanks for any comments. I will also check for codes and will report back.

Hi jagnut,

I don't believe those ground wires are related to the ABS system. If I recall correctly, they help protect the wheel bearings from damage due to static electricity and other potential currents. See pdf page 21 of this document:

Timken Bearing Damage Analysis

I have to run, but the first questions that come to mind are:

1. Have you checked all your fuses?

2. Have you checked the Vehicle Condition Monitor (VCM) for any stored Diagnostic Trouble Codes (DTCs)? To do so, turn the key to position II but do not start the engine. Press and release the VCM button on the trip computer to the right of the steering wheel and watch for a message to appear in the odometer window below the speedometer. Write down any message exactly as it appears and report it here and we'll try to help.

3. Have you tried swapping your ABS relays with other ones? IIRC, the ABS relays are mounted on the left blower motor housing behind the driver's knee bolster/underscuttle. You could try swapping in any similar relays from the ones along the right firewall in the engine bay, just keep track of which relay started in which position.

Cheers,

Don

Thanks for that Don, page 21 of the .pdf explains in full ...always wondered what those braids were for! :icon_dunce:

Larry

DON THANKS, i just pulled codes and got 34 for left rear sensor..followed the trail and found the sensor cable cut into at the hole that is suppose to have a rubber grommet to protect from chafing. The sensor had been replaced before because of the zip ties. Can I splice back together? The prices are obscene for this sensor and not available in most places. DBC6247...anyone have a used one? I will try to find one at a salvage yard. Any help greatly appreciated.

Hi jagnut,

Yes, you can usually splice the wires back together. It's best to slip some heat shrink tubing sections over the wires and down the main harness, twist and solder the wires, then position the sections of heat shrink tubing to cover the solder joints, shrink them with a heat gun, then slide the section of heat shrink tubing that you slid down the main harness over both solder joints and shrink it to cover the entire repair (two layers of heat shrink tubing is even better). I you don't solder and/or don't have heat shrink tubing, you can use the crimp-style connectors to carefully crimp the wires together (don't squeeze too hard on your crimping pliers - you just need to crimp the connector until the joint between the wire and connector is air-tight and can't be pulled free with a moderate tug), then insulate the repair with electrician's tape. Your goal is to add minimal resistance to the circuit.

Cheers,

Don

Thanks for all your help.Best Regards

Your advice on repair worked like a charm....No abs speedo working and best of all I did not have to purchase a $300.00 part!!!! Thanks again

Click the thanks button on Don's post whydontcha !

:icon_that:

Larry