C0042 — Brake Pedal Position Sensor Circuit A (Subfault)

vehicle

Is it safe to drive?

Drive with caution The base brakes usually still work, so careful driving is possible — but ABS and stability control are disabled, which lengthens stopping distances on slippery roads. Fix promptly and avoid harsh driving.

How to diagnose with an OBD scanner

Read the code and freeze frame Connect an OBD2 scanner, confirm C0042 is stored, and save the freeze frame data — it shows engine conditions when the fault was detected.
Check for companion codes and TSBs Related codes often reveal the real root cause. Also check manufacturer technical service bulletins (TSB) for your make and model — many C0xxx issues have factory fixes or software updates. Search by VIN on the manufacturer site or nhtsa.gov.
Inspect wiring and connectors Visually inspect the wiring harness and connectors related to the ABS / stability control for damage, corrosion, chafing or poor contact.
Subsystem check Read all four wheel speed PIDs while driving slowly — the faulty sensor drops out or reads implausibly.
Subsystem check Inspect the sensor and tone ring for metal debris and damage near the hub.
Verify the repair Clear the code, complete a full drive cycle including the conditions from the freeze frame, and confirm C0042 does not return.

Approximate repair cost

Repair cost depends on which component actually failed. Typical scenarios for C0042 (parts and labor, USD, independent shop rates): ABS module repair or replacement: $400–$1,200; Repair sensor wiring: $80–$250; Replace a wheel speed sensor: $120–$350. Overall, fixing C0042 usually costs between $80 and $1,200. An accurate diagnosis before buying parts saves money — the most expensive scenario is rarely the first one to check.

Common questions

What are the symptoms of C0042?

Drivers most often notice: ABS or ESC warning light on, speedometer or cruise control issues, brake pedal pulsation changes, ABS not operating during hard braking.

How do I diagnose C0042 myself?

Start with a scan: confirm C0042, save the freeze frame and note any companion codes. Then inspect the wiring and connectors related to the ABS / stability control, and verify the suspect component against live data before buying parts.

Will C0042 clear itself?

Sometimes C0042 clears after a few drive cycles if the fault was intermittent — for example a loose connector or a tank of bad fuel. The underlying cause usually remains, so the code tends to return. Clear it once; if it comes back, diagnose rather than erase it repeatedly.

Is it safe to drive with C0042?

The base brakes usually still work, so careful driving is possible — but ABS and stability control are disabled, which lengthens stopping distances on slippery roads. Fix promptly and avoid harsh driving.

How much does it cost to fix C0042?

ABS module repair or replacement — $400–$1,200; Repair sensor wiring — $80–$250; Replace a wheel speed sensor — $120–$350. Exact cost depends on the root cause, your vehicle and local labor rates — a proper diagnosis is the cheapest first step.

C0042 — C0042 — Brake Pedal Position Sensor Circuit A (Subfault): Causes, Symptoms & Fix

When your scan tool pulls code C0042, the vehicle's control unit is reporting a fault in the brake pedal position sensor circuit — specifically the "A" subfault channel. This sensor plays a role in the ABS and electronic stability control system, feeding data about where your foot sits on the brake pedal to modules that need to know driver intent. If the signal goes out of range, drops to zero, or stops making sense, the ECU logs C0042 and turns on the dashboard warning.

The system does not wait for a catastrophic failure to set this code. Instead, it monitors the sensor voltage and behavior across multiple drive cycles. When readings consistently fall outside the factory calibration window, C0042 gets stored alongside freeze frame data — a snapshot capturing RPM, vehicle speed, engine load, and temperature at the exact moment the fault triggered. That snapshot is your best starting point because it tells you whether the problem happens at low speed, high load, cold start, or under braking.

What happens next depends on which component inside the circuit actually failed. The sensor itself, its wiring harness, the connector terminals, or even the ABS control module can all produce the same diagnostic code. That is why a systematic approach matters before spending money on parts.

Symptoms

ABS warning lamp stays illuminated on the instrument cluster
Electronic stability control (ESC) inactive or disabled message appears
Cruise control refuses to engage or disengages unexpectedly
Brake pedal feel changes — either too firm, too soft, or inconsistent
Anti-lock braking does not activate during emergency stops
Speedometer readings become erratic or jump around

Causes

Wheel speed sensor failure — the most frequent culprit behind C0042-related codes
Damaged wiring harness or corroded connector at the sensor or module
Blown fuse supplying low voltage to the ABS circuit
Failed ABS control module or internal pump motor fault
Metal debris or physical damage to the tone (reluctor) ring mounted on the hub
Poor ground connection at the sensor circuit

How to Diagnose

Plug in an OBD2 scanner and confirm C0042 is an active or pending code. Record the freeze frame data — note the speed, load, and temperature values recorded when the fault first appeared.
Pull all related codes from every module. Coexisting P-codes or C-codes often point directly to the root cause. Cross-reference any relevant technical service bulletins for your specific make and model, as manufacturers sometimes publish software updates or known fixes for C0xxx fault families.
Perform a visual inspection of the entire wiring path between the sensor and the ABS module. Look for chafed insulation, bent pins, moisture intrusion, and any signs of corrosion that could interrupt the signal.
Monitor live wheel speed data on the scanner while driving slowly in a safe area. A failing sensor drops out intermittently or shows implausible values compared to the other three wheels.
Remove and physically inspect the tone ring and sensor at each wheel. Metal shavings, missing teeth on the ring, or a cracked sensor housing will show up here.
Clear C0042 after your inspection, complete a full drive cycle that recreates the freeze frame conditions, and verify the code does not return. If it does, the fault is confirmed and you can proceed to repair with confidence.

Repair Options

Replace wheel speed sensor (single): $120–$350 parts and labor
Repair or splice damaged wiring harness: $80–$250 depending on accessibility and connector condition
Rebuild or replace ABS module and pump assembly: $400–$1,200 depending on vehicle and whether you choose remanufactured or new

How Much Does It Cost to Fix C0042?

The total bill hinges on which part is actually at fault. In most cases, the wheel speed sensor itself is the problem — and that is the least expensive fix on the list. Wiring repairs fall in the middle range, while an ABS module replacement represents the high end. Expect to pay somewhere between $80 and $1,200 for a complete resolution. The single most important step is an accurate diagnosis before purchasing parts — the most expensive scenario is almost never where you should start.

Can You Drive with C0042?

Your conventional brakes will continue to function. However, the anti-lock system and stability control will be offline, which means stopping distances increase on wet, icy, or uneven surfaces. Drive with caution, avoid aggressive braking maneuvers, and prioritize getting the code diagnosed and repaired as soon as possible.