When the ABS and ESP warning lights come on at the same time, the cause is a faulty wheel speed sensor in about 80% of cases. In that situation the ABS control module disables ESP along with ABS, so both lamps light up together. Less often, the culprit is the tone ring, the wiring, or the hydraulic unit.
Why ABS and ESP Shut Off Together
ESP runs on wheel speed signals generated by the ABS system. As soon as one sensor stops delivering a valid signal, the ABS control module deactivates both systems—ABS and ESP. That’s why the two indicators come on simultaneously.
On its own, this is not a sign of a failed hydraulic unit. Hydraulic units rarely break, and starting the diagnosis there makes no sense—it only adds unnecessary expense.
Likely Causes
| Cause | How It Shows Up | Likelihood |
|---|---|---|
| Wheel speed sensor | Usually one wheel; the fault memory shows the axle and position. Code 5DF1 | Most common, around 80% |
| Tone ring on the hub bearing | Rust or physical damage, often after a bearing replacement | Less common |
| Wiring to the sensor | Marten damage or chafed insulation | Less common |
| ABS control module / hydraulic unit | Electronic or mechanical failure inside the unit | Rare, expensive |
Wheel speed sensors fail more often than anything else here—usually just one wheel. The tone ring on the hub bearing falls victim to rust or breaks apart after a bearing replacement. Wiring to the sensor gets chewed up by martens or chafes through where it touches the body.
What Service Shops See in Practice
The most common reason for a visit is a failed sensor on one wheel. The fault memory points straight to the axle and the position, so tracking down the bad component doesn’t take long. In real-world failure statistics, the hydraulic unit ranks last.
Diagnosis: Where to Start
The first meaningful step is to read the ABS fault memory and the live data. Only then do you judge which component is actually at fault. The fault memory shows the wheel position: VL (front left), VR (front right), HL (rear left), HR (rear right).
5-Minute Quick Check
- Read the ABS fault memory—it will point to the wheel position.
- Visually inspect the sensor and test it with a multimeter.
- Check the tone ring on the hub bearing for rust.
- Check the battery voltage: it should be above 12.4 V.
Diagnostic Equipment
Two tools fit this job:
- ANCEL AD310 — a corded OBD2 scanner that reads and clears fault codes, including live data and freeze-frame.
- Fluke 115 — a True RMS multimeter for measuring voltage, resistance, and continuity on sensors, connectors, and wiring.
The tool list is neutral: no obligation to buy, no prices, no ratings.
Contradictions in the Source Data
- The ANCEL AD310 is described as a tool for reading engine codes, yet it appears in a diagnostic section for ABS/ESP—that is, the chassis and brake control module. Keep that mismatch in mind when reading fault codes in the brake circuit.
- On one hand, the sensor is listed as Plug & Play with “learning usually not required.” On the other, both the quick check and the fault description itself assume you’ll be working with the control module and its fault memory. The requirement to read fault codes and the absence of any learning procedure indirectly contradict each other.