How to Test ABS Sensors on a Truck Without a Scan Tool

Knowing how to test ABS sensor circuits with a multimeter keeps good sensors on the truck. With the ignition off, read each sensor's resistance and insulation to ground at the ABS controller connector; then raise the wheel, spin it by hand and read AC volts. Weak output sends you to the gap, bearing play and tone ring first.

Last updated: November 26, 2026

Key takeaways

• Start at the ABS controller connector: Bendix tests there first to spare the wheel-end connector seals, and WABCO's TP-99145 starts there too.
• Pass windows depend on the sensor: 1,200-2,700 ohms for a Bendix WS-24 at 0-100°F, 900-2,000 ohms for the WABCO sensors in TP-99145.
• Resistance proves only the circuit; a wheel turned by hand at half a revolution per second must also give 0.25 V AC (Bendix) or 0.2 V AC (WABCO).
• Passing at the sensor's own plug but failing at the controller puts the fault in the harness or a connector.

A passive wheel speed sensor is a coil, a pole piece and a magnet in one housing that makes its own AC voltage. The exciter, also called the tone ring or tooth wheel, is a steel ring with evenly spaced teeth that turns with the hub. Bendix's WS-24 service data sheet SD-13-4860, filed with NHTSA, explains the signal: each tooth and the space beside it induce one AC cycle, and the controller turns cycle frequency into wheel speed using the tooth count programmed into it. The voltage only shows signal strength, and it rises as the gap closes.

The steps below fit two-pin passive sensors such as the WS-24 and the WABCO sensors in TP-99145; a powered (active) sensor is checked to its own maker's procedure. For waveforms and sensor types in more depth, read our ABS sensor resistance, signal and tone ring guide.

What should you check before the meter comes out?

Without a scan tool, the dash lamps narrow the search. Under FMVSS 121, S5.1.6.2, the tractor ABS lamp lights for a bulb check at key-on and then stays lit while a malfunction exists or was stored at the last key-off. Tractors built from March 1, 2001 add a separate lamp for trailer ABS faults, and trailers built from March 1, 1998 carry a yellow ABS lamp on the left side, near the rear.

A lamp that stays lit is a repair item. 49 CFR 393.55 requires ABS on truck tractors built on or after March 1, 1997 and on other air-braked commercial vehicles from March 1, 1998, and 49 CFR 396.3 requires the parts listed in Part 393 to be in safe and proper operating condition at all times.

Bring a multimeter with an AC volts range, chocks, safety stands and the controller's pin table. TP-99145 forbids working under a truck held only by jacks and lists different pin pairs for each WABCO controller version.

How to test ABS sensor circuits at the controller connector

The order below combines Bendix's data sheet, WABCO's TP-99145 sensor test bulletin and Navistar's general wheel speed sensor troubleshooting article, also filed with NHTSA.

1. Secure the truck. Chock the wheels on level ground, turn the ignition off and set the parking brakes.
2. Open the controller connector. Unplug the harness connector carrying the suspect sensor at the ABS controller and look for corrosion, bent terminals and loose pins.
3. Read resistance across the sensor's two pins. A WS-24 passes at 1,200-2,700 ohms at ambient temperatures of 0-100°F (−18 to 38°C); the WABCO sensors in TP-99145 pass at 900-2,000 ohms.
4. Test insulation from each pin to the sensor case or a clean chassis ground. TP-99145 accepts only an open circuit; any measurable resistance means a short to ground in the sensor or its cable.
5. Spin the wheel. Raise it, release the parking brakes and turn it by hand at half a revolution per second or faster, 30 rpm in WABCO's wording, reading AC volts across the same pins: Bendix wants at least 0.25 V, WABCO 0.2 V.
6. Close the gap and repeat. If output is low, push the sensor gently until it touches the ring and measure again. If it stays low, Bendix and Navistar replace the sensor, Bendix with a new clamping sleeve; TP-99145 sends you to WABCO's customer care line.
7. Follow a failed reading outward to each connector toward the wheel and finally the sensor's own plug, cleaning wheel-end connectors before opening them so their seals survive.

Readings inside the limits at the controller clear the sensor, and Bendix then sends you to pinched wires, loose pins and exposed wires in the harness and controller connector. Each window belongs to its own document: an older Bendix WS-20 was rated at 2,000-5,000 ohms at room temperature, so take another sensor's limits from its maker's current data.

Bendix WS-24 or WABCO sensor: which limits apply?

Pass limits in two OE wheel speed sensor procedures

Check	Bendix WS-24 (SD-13-4860, 2019)	WABCO sensors (TP-99145, 2018)
Resistance across the pins	1,200-2,700 ohms at 0-100°F; 1,575-2,100 ohms at 20°C	900-2,000 ohms; open circuit from each pin to ground
AC output, wheel turned by hand	0.25 V minimum at half a revolution per second or faster	0.2 V minimum at 30 rpm
Gap and wheel end	0.015 in (0.38 mm) maximum gap	Check bearing end play and tooth wheel if signal errors continue

Sensor or harness: how do you tell them apart?

In TP-99145, a sensor that passes at its own plug but fails at the controller connector means the harness or a connector is at fault; check the extension cable for broken wires and wear from moving parts. Navistar tests the chassis harness alone, with sensor and controller unplugged: each wire must read under 5 ohms end to end and over 100,000 ohms to chassis ground.

If you can read which wheel the stored code names, Navistar settles a fault that keeps returning by temporarily swapping the left and right sensor leads at the controller and re-testing: a fault that changes sides belongs to that harness or wheel end, while one that stays put points to the controller.

How close does the sensor sit to the tone ring?

On the WS-24 the gap sets itself: the clamping sleeve lets the sensor slide under force and hold when the force stops, so a sensor pushed fully home is nudged back by the hub exciter and normal bearing play into a running clearance. Bendix's drawing shows a typical 100-tooth exciter with a 0.015 in (0.38 mm) maximum gap, and the data sheet rates output at 0.350 V AC at 100 Hz, about 7 mph, with a 0.028 in gap. Other sensors and axles have their own figures in their makers' documents.

TP-99145 reads the gap through the AC test, filing low output under an excessive air gap. Bendix adds that excess wheel end play can push the sensor away and cost ABS or stability control, and Navistar checks end play, tone ring corrosion and sensor grip before condemning a sensor. A tone ring can upset ABS without setting a code: in a 2020 technician thread in NHTSA's service bulletin library, false ABS activity from 25 mph up on a 2005 Freightliner M2 traced to a right front ring bent at one spot.

Which workshop habits bring the ABS lamp back?

• Reusing the sleeve. Bendix's procedure renews the clamping sleeve with every WS-24 and warns that reduced retention lets the sensor move and set ABS codes.
• Hammering the sensor home. Push it gently until it bottoms on the tone ring face; Bendix says not to strike it.
• Leaving the lead loose. Bendix secures the cable to the knuckle or axle housing 3-6 inches (76-152 mm) from the sensor and puts dielectric grease on both connector halves before the lock tab snaps home.
• Fitting a ring with another tooth count. Bendix notes that the controller calculates speed from the tooth count programmed into it, so a replacement ring must match the one removed.
• Clearing the code and stopping there. Bendix's check drive reaches at least 15 mph with several left and right turns and stops; the ABS lamp must stay off afterward.

Which VADEN parts fit a wheel-end ABS repair?

Corrosion or a bent tooth calls for a new ring. Among VADEN's ABS sensor rings, the 1300 03 006 ring for Volvo and Renault Trucks hubs is listed with a 135 mm inside and 165 mm outside diameter and 100 holes, replacing Volvo 22537018 and Renault Trucks 7422537018. The 1100 03 001 ring for Mercedes-Benz is listed with 100 holes, 153/172 mm inside and 176/195.5 mm outside diameters, and replaces 942 356 00 15, 942 356 03 15 and 942 356 07 15. Our wider ABS sensors category adds sensor holders for Volvo and Renault Trucks. Match diameters and hole count to the ring you remove, and see how the full ABS system controls wheel slip.

Frequently Asked Questions

Can you check an ABS sensor without raising the wheel?

Partly. The resistance and insulation checks at the controller connector need only the ignition off, the parking brakes on and the wheels chocked, so the tire stays on the ground. The output test cannot: Bendix and WABCO both lift the wheel, release the brakes and turn it by hand to prove the sensor sees the ring.

Does temperature change ABS sensor resistance?

Yes, enough to fail a good sensor. Bendix rates the WS-24 at 1,575-2,100 ohms at 20°C and 1,200-2,700 ohms at 0-100°F ambient, but from −40 to 220°C the same sensor can read 1,100-3,400 ohms. Let a hot hub cool after a long run or heavy braking before you judge a reading.

How often should wheel speed sensors be inspected?

Bendix sets two intervals for the WS-24. The visual check of wiring, connectors, sensor and mounting bracket is listed at 3 months, 25,000 miles, 900 operating hours or the chassis lubrication interval. The operational test, with the wheel raised and spun for an AC reading, is listed at 12 months, 100,000 miles or 3,600 operating hours.

Should traction control be off before you spin a drive wheel?

Bendix requires it for any maintenance in which a lifted drive-axle wheel turns: disable automatic traction control first and confirm that the ATC lamp is on. WABCO's TP-99145 runs its output test with the ignition off and the controller connector unplugged, so the controller never sees the spinning wheel.

Does a new sensor need a new clamping sleeve?

Yes, in Bendix's procedure, and the type matters: sleeve 5006849 must not be used with the WS-24. The stainless sleeve K152407 requires high-temperature silicone- or lithium-based grease on the sensor body; with sleeve 5012878, Bendix recommends that grease inside the mounting block. Navistar also renews the sleeve when a sensor is not held firmly.