Wheel Speed Sensor: Description and Operation
ABS wheel sensor wiring -January 1996Customers have complained that the brake pedals in model year 1996 cars pulse, and that there is some noise, when braking at low speeds. However, no reduction in braking performance or other faults have been reported. If the above occurs, it is due to the ABS system carrying out a self-diagnosis at low speed, which can be a result of high resistance in one of 4 cable splices in the front wheel sensor cable harness. The cables have a thin plastic film on the inside of the insulation to make them more flexible, and there may be a residue of this plastic film in the cable splice crimp. The wiring has been remedied in production from February 1996. The correct material, and cars that have been remedied, are marked with a green dot (decal or paint) under the fusebox cover on the white edge of the integrated relay/fusebox. This Service Bulletin describes how to cut and re-splice suspect cable splices.
After re-splicing the ABS system should be tested according.
Replacing wiring (not natural gas powered cars)
^ Place the new cables (A and B) on the gutter.
Note: Right-hand wiring (A=long). Left-hand wiring (B=short).
^ Cut off the old wiring at the wiring ducts.
^ Remove cables from the clips.
^ Tape the old and new ABS cables together, first (A) then (B), so that the new cable can be pulled through by the old cable.
^ Raise the car.
^ Remove front wheels
^ Remove ABS cable from ABS sensor at the front wheels.
^ Remove ABS cable from bracket and from clip.
^ Carefully pull cable so that new cable is pulled through with the old cable.
Caution: The new ABS cable must be as long as the old one.
^ Connect the new cable to ABS sensor on right front wheel.
Note: Do not connect the left ABS sensor to the left wheel before function testing the right sensor.
^ Install cable in bracket.
^ Install cable in clips.
^ Install wheels.
^ Lower car
^ Route the right cable between drain hose and fireball.
^ Remove the 3 middle gutter screws.
^ Slacken off the 2 outer gutter screws a few turns.
^ Install 5 clips on the edge of the firewall. (Start with a clip on each side of the stamped chassis number.)
^ Install the remaining clips.
^ Route wiring from the right side to the cable duct by the left wheel arch.
^ Open the cable duct.
^ Pull the new wiring into the cable duct through the opening at the firewall.
Note: Remember which cable comes from each side.
^ Locate two twisted cable pairs, 1 brown/white and 1 black/white.
^ Locate two twisted cable pairs, 1 brown and 1 black.
Caution: The two twisted cable pairs that go in the cable duct to the 25-pin ABS connector can be the same color (brown/black). It can be difficult to determine which wheel a cable pair comes from. Therefore connect the cable pairs to the new ABS cables (A or B) one at a time without crimping or soldering them as follows, and test with the Volvo Scan Tool (ST) according to (A21). Rotate a wheel and read the instrument. Correctly connected cables will give a reading for the wheel which is rotating. Then splice/solder as follows.
Note: Cut off and splice one cable at a time.
^ Cut off the cables, one by one as close to the firewall as possible.
^ Splice the cables as follows: Black/white to black on the left-hand wiring. Then splice brown/white to brown on the left-hand wiring. Then splice black to black on the right-hand wiring. Then splice brown to brown on the right-hand wiring.
Joining
^ Thread 2 heat-shrink tubes onto the new ABS sensor cables.
Cut cable splice on both cables
Strip insulation on the 4 cable ends 13 mm with pliers 951 2620.
There may be a thin plastic film residue on the white (tinned) conductor units.
Untwist the stripped cable ends a little and twist them together again. For safety reasons, do the same with all four stripped cable ends.
Note: The (brown/black) cable pair are twisted around each other. It is important that paired cables are paired in the same way as earlier, before they are re-spliced. They should be twisted approximately 3 turns per 100 mm.
Splice the same cable ends that were previously spliced.
Insert crimping sleeve 967777 into the crimping tool 951 2649, in crimping slot "A" (This is easier on a workbench).
Squeeze the crimping tool a little to secure the crimping sleeve in the tool.
Take the crimping tool with crimping sleeve to the car
Put both cable ends in the crimping sleeve in the tool. Insert cables in crimping sleeve so that their insulation comes up to but not into the crimping sleeve. Both cables should be inserted from the same direction (parallel).
Note: Insert cables in the crimping tool on the side without text!
Squeeze crimping sleeve into place.
Check by hand that crimping sleeve is secure.
When one cable pair has been spliced, cut and splice the remaining cable pair.
When the cable ends are joined, solder the tops of the conductors outside the crimping sleeves. This work may only be carried out by a professional, accustomed to soldering electrical components.
Set up an extractor by the soldering site.
Take care of adjacent cables. If necessary set up a heat shield.
Heat the crimping sleeve/conducting unit ends with the soldering iron. Heat thoroughly. Apply solder so that some runs into the crimping sleeve covering the conducting units.
Installing heat-shrink tubing on cable splice
^ Fold both cable splices as illustrated (arrow).
^ Carefully pull the heat-shrink tubing over the soldered cable splices. (The cable ends should be inside the tubing).
^ Heat the heat-shrink tubing
Note: The heat-shrink tubing is intended to provide good electrical insulation. Only one cable should protrude from the ends of the heat- shrink tubing.
^ Hold a putty knife behind the heat-shrink tubing and heat at close range using a hot air gun. Heat heat-shrink tubing quickly to avoid overheating the cable insulation.
Caution: The heat-shrink tubing should be totally crimped around the crimping sleeve. The ends should be sealed.
^ If necessary set up a heat deflector.
^ Twist the cables as much as possible before reinstalling into cable duct.
^ Even out excess in the right cable at the spring strut turrets and position the cable in clips.
^ Close the cable duct.
^ Install screws for gutter.
^ Pull the cable tight in the cable duct at the right spring strut turret. Use a tie strap.
^ Pull both cables taut in cable duct at the left spring strut turret. Use a tie strap.
Checking ABS system after repair Method
Note: It is important that the following checks are made in the correct order.
^ Connect Volvo Scan Tool (ST). Select: MONITOR TEST/ENTER/SCROLLING LIST/ENTER/LIST 1/ENTER/
^ Rotate right front wheel.
^ Check signal from right front wheel.
^ Connect left wheel sensor. (Connect connector at left ABS sensor.)
^ Rotate left front wheel.
^ Check signal from left front wheel.
^ Test drive the car.
^ Carry out a brake test.
^ Use the Volvo Scan Tool (ST) to check that there are no diagnostic trouble codes (DTCs).