C0042 on 2016-2020 Ram 3500: Brake Pedal Sensor Calibration Fault Explained

What's Unique About the 2016-2020 Ram 3500

Ram trucks of this era use a sensitive electronic brake pedal position sensor that requires precise calibration to function. Unlike older, simpler mechanical brake light switches, any service involving this sensor—including replacement, or sometimes even just disconnecting the battery—can trigger this code if the electronic 'relearn' or calibration procedure is not performed. This procedure requires a specific diagnostic scan tool (like the dealer's wiTECH, or DIY-friendly tools like AlfaOBD), making it a common point of failure for DIY repairs if the final step is missed.

Diagnostic Flowchart

Tap your situation to follow the diagnostic path that matches what you're seeing on this vehicle. 👇

Generation note: This range covers the end of the fourth generation (2016-2018) and the beginning of the fifth generation (2019-2020) Ram 3500. The Brake Pedal Position Sensor and the requirement for calibration are common to both generations within this period, though specific part numbers may vary.

Symptoms You May Notice

• ABS warning light is on
• Electronic Stability Control (ESC) or traction control warning light is on
• "Service Electronic Braking System" message on the instrument cluster
• Cruise control will not engage
• Brake lights stay on continuously, even when the truck is off, potentially draining the battery
• Brake lights do not turn on when pressing the pedal
• Remote start may be disabled

Most Likely Causes

1. Lost or Missing Calibration 🔴 High Probability Calibration can be lost after replacing the battery, the sensor itself, or the ABS module. TSB #S1808000152 specifically calls out "Brake Pedal Missing Calibration" (C0042-54) for this issue.
   How to confirm: Using a capable scan tool (like wiTECH or AlfaOBD), attempt to run the "Brake Pedal Calibration" routine in the ABS module's functions. If the procedure completes successfully and the code clears, this was the cause.
   Typical fix: Perform the brake pedal position sensor calibration using a compatible scan tool. This is often found in the ABS module's 'miscellaneous functions' or 'functional tests'. A YouTube user demonstrated this exact fix for brake lights stuck on, successfully using AlfaOBD. 🎬 Watch: How to calibrate the sensor and fix stuck brake lights.
   Est. part cost: $0
2. Faulty Brake Pedal Position Sensor (BPPS) 🔴 High Probability → Shop Brake Pedal The sensor is a sensitive electronic component that is a known high-failure item, as evidenced by TSBs and widespread owner reports. Some users on forums report that aftermarket sensors may fail to calibrate correctly, recommending OEM parts.
   How to confirm: Use a scan tool to monitor the BPPS voltage in the live data stream while pressing the pedal. A healthy sensor shows a smooth voltage change (e.g., ~0.5V to ~4.5V). If the voltage is stuck, erratic, or doesn't change, the sensor is bad.
   Typical fix: Replace the Brake Pedal Position Sensor and immediately perform the calibration procedure.
   Est. part cost: $20-$60
3. Damaged Wiring or Connector 🟡 Medium Probability The wiring and connector are located in the driver's footwell and can be susceptible to damage from physical stress, moisture, or improper diagnostic probing (piercing wires).
   How to confirm: Visually inspect the sensor's connector and nearby wiring for corrosion, bent pins, or physical damage. A detailed YouTube video of a 2018 Ram 3500 repair showed that a damaged pigtail from previous diagnostic probing (which broke the 5V reference wire internally) was the ultimate cause, even after the sensor was replaced. The mechanic had to source a salvage yard pigtail 🎬 See this walkthrough on diagnosing damaged wiring and sensor issues. to fix it.
   Typical fix: Repair the damaged wiring or replace the connector pigtail, then perform the sensor calibration.
   Est. part cost: $15-$40

Rare But Worth Checking

• Failing Anti-Lock Brake System (ABS) Module: → Shop ABS Control Module This is rare and should only be considered after the sensor, its calibration, and wiring have been definitively ruled out. A Reddit user with a Ram 2500 experiencing C0042-11 along with all four wheel speed sensor codes was advised it was likely a module issue. In some cases, dirt and debris in the main ABS module connector can cause communication issues mimicking a module failure; 🎬 Watch: What to do if your ABS module or HCU fails. cleaning this connector has resolved issues for some owners.

Diagnosis Steps

1. Connect a scan tool capable of reading Ram ABS codes and live data (e.g., AlfaOBD, Autel, wiTECH).
2. Read all DTCs from all modules. Note any sub-codes for C0042 (e.g., -54, -11, -12) and any accompanying codes like P0572 or P057B.
3. Using the scan tool, navigate to the ABS module's live data for the Brake Pedal Position Sensor.
4. Observe the sensor's voltage or percentage reading while slowly pressing and releasing the brake pedal. The reading should be smooth and consistent, typically sweeping from a low voltage (~0.5V) to a high voltage (~4.5V). Any jumps, flat spots, or lack of change indicates a problem.
5. Attempt to perform the 'Brake Pedal Calibration' or 'Brake Pedal Position Sensor Learn' routine. This is typically found in the ABS module's 'Miscellaneous Functions'. CRITICAL: Do not press the brake pedal during this procedure unless prompted. The scan tool will confirm if the procedure passed or failed.
6. If the calibration passes and the code does not return, the issue was lost calibration. Clear any remaining codes and test drive.
7. If calibration fails or the code returns immediately, visually inspect the sensor, its connector, and the wiring harness for any physical damage, corrosion, or looseness. Pay close attention to wires that may have been pierced by test probes in the past.
8. If the wiring appears intact, the next logical step is to replace the Brake Pedal Position Sensor with an OEM part. It is located on the brake pedal support bracket.
9. After installing the new sensor, you MUST perform the 'Brake Pedal Calibration' routine again. This is not an optional step.
10. If the code still persists after replacing the sensor and attempting calibration with known-good wiring, further diagnosis of the ABS module and its main connector may be required.

Parts You'll Likely Need

• Brake Pedal Position Sensor (OEM #68273742AA) — This sensor is the most common point of failure for code C0042. It can fail internally or require replacement after its calibration is lost and cannot be relearned. Using an OEM Mopar part is highly recommended as some aftermarket versions may not calibrate correctly.
  Trusted brands: Mopar
  OEM price range: $20-$50
  Aftermarket price range: $15-$40

Related Codes That Often Appear With This One

• P057B — Brake Pedal Position Sensor Circuit Performance. This code is directly related to the sensor's function and is mentioned in TSB #S1808000152 alongside C0042.
• P1572 — Brake Pedal Stuck. Also mentioned in TSB #S1808000152, this can be triggered by the faulty sensor data.
• P0572 — Brake Switch 'A' Circuit Low. TSB #9003530 links this code with C0042, pointing to the same brake pedal sensor system. A user on RamForum.com reported this code appeared after a failed calibration attempt by a shop.

Technical Service Bulletins (TSBs) & Recalls

• S1808000152: Mentions C0042-54 Brake Pedal Missing Calibration as a possible DTC after a module replacement or software update, and emphasizes that the pedal learn procedure must be performed.
• 9003530: Recommends checking the Brake Pedal Home Position setting with a wiTech tool for vehicles with DTC C0042 or symptoms like brake lights staying on.

Platform-Specific Known Issues

• TSB #S1808000152 was issued for multiple DTCs including C0042-54 "Brake Pedal Missing Calibration", indicating this is a recognized issue by the manufacturer, particularly after a PCM replacement or update.
• TSB #9003530 addresses complaints of brake lights staying on or cruise control not setting, linking them to DTC C0042 and the need to check the Brake Pedal Home Position setting with a wiTech scan tool.
• Widespread owner complaints on forums like HDrams.com and CarComplaints.com mention the "Service Electronic Braking System" warning in relation to ABS system failures on these trucks, which often begins with codes like C0042.

Mechanic-Grade Diagnostic Values

• Brake Pedal Position Sensor (BPPS) Signal Voltage — expected: A smooth, continuous sweep from ~0.5V (pedal released) to ~4.5V (pedal fully depressed).. Failure: Voltage is stuck at 0V, 5V, or another value; voltage jumps erratically; or there is no change when the pedal is pressed.
• BPPS Circuit Continuity — expected: Resistance below 5.0 Ohms on the signal, supply, and ground wires between the sensor connector and the ABS module connector.. Failure: Resistance is above 5.0 Ohms, indicating an open or high-resistance fault in the wiring harness.
• BPPS 5V Reference Voltage at Sensor Connector — expected: ~5.0V with key on, engine off.. Failure: Voltage is significantly lower than 5V or is absent, indicating a wiring or ABS module fault.

Hidden / Shadow Codes Worth Checking

• C0042-62: Brake Pedal Position Sensor - Signal Compare Failure. This indicates the ABS module sees a discrepancy between expected and actual sensor signals. (see via Professional-grade scan tools capable of reading manufacturer-specific sub-codes.)

Scan Tool Commands That Help

• AlfaOBD: Brake Pedal Calibration — This is a mandatory procedure after replacing the BPPS or after the battery has been disconnected. It is found by connecting to the ABS module, selecting the 'procedures' icon (car with hood popped), and choosing 'Brake Pedal Calibration'.
• wiTECH (Dealer Tool): Brake Pedal Position Sensor Learn / Brake Pedal Calibration — Used by dealerships for the same mandatory calibration. It is located in the ABS module's 'Miscellaneous Functions' or 'Functional Tests' menu.
• wiTECH (Dealer Tool): Initialize ECU — In some complex cases, especially after module replacement or significant wiring repair, the ABS module itself may need to be re-initialized before it will accept the brake pedal calibration.

Wiring & Ground Locations

• ABS Module Connector (2018 HD Example) — At the main harness connector for the ABS control module, typically located in the engine bay.. Allows for definitive testing of the entire circuit from the module side. Pin 29 is the 5V sensor feed, Pin 14 is the sensor return (ground), and Pin 11 is the signal wire. Testing here can isolate a wiring fault from a sensor or module fault.
• Brake Pedal Position Sensor Connector — Directly on the sensor, which is mounted by the brake pedal arm in the driver's footwell.. This is the most common point for physical damage, corrosion, or loose pins. A bad connection here is a primary cause of C0042. A technician on YouTube identified the middle pin as ground and one of the outer pins as the 5V feed on a 3-wire connector.

Real Owner Repair Stories

• YouTube channel '3Ts Mobile Mechanic' (2018 Ram 3500 Diesel) — C0042 'Brake Pedal Missing Calibration' code active and stored, inability to calibrate the sensor.
  ❌ Tried (didn't work) A previous shop replaced the sensor but could not calibrate it., Initial attempts to repair the visibly damaged connector pigtail failed.
  ✅ What actually fixed it The 5V reference wire was broken internally inside the harness insulation due to a previous technician piercing the wire with a test probe. The fix required replacing the entire connector pigtail with a part from a salvage yard and carefully soldering the connections. After the wiring was fixed, the 'Brake Pedal Calibration' passed, but the code remained until the 'Initialize ECU' function was also run on the ABS module.
• YouTube channel 'Boosted Motorsports 2' (Ram 1500 (4th Gen)) — Brake lights were stuck on after accidentally breaking and replacing the brake pedal position sensor.
  ❌ Tried (didn't work) Replacing the sensor with a new Mopar part did not solve the problem on its own.
  ✅ What actually fixed it The new sensor required calibration. The owner used the AlfaOBD app with an OBDLink MX+ adapter to connect to the ABS module and run the 'Brake Pedal Calibration' procedure. This immediately fixed the issue, and the brake lights began functioning correctly.
• YouTube channel 'Dallas Auto Diag' (2018 Dodge Charger (shares similar sensor design)) — C0042-12 'Circuit Short to Battery', brake lights stuck on, car would start without pressing the brake.
  ❌ Tried (didn't work) The owner had replaced the sensor with an aftermarket part.
  ✅ What actually fixed it The new sensor was installed incorrectly. The plastic actuator arm on the sensor was on the wrong side of the metal stopper tab on the brake pedal assembly. This held the sensor at its maximum reading (5V) constantly. Reinstalling the original OEM sensor in the correct physical orientation resolved the code without needing calibration.

OEM Part Supersession History

• 68273742AA → N/A — This appears to be the current and most commonly cited part number for the 2016-2018 model years.

Model Year Variations Within This Range

• 2019-2020 (5th Gen 'DT'): The 5th generation Ram trucks use a different brake pedal position sensor (P/N 68340480AB) which is not interchangeable with the 4th generation part (68273742AA). While the operating principle and need for calibration remain the same, the physical part is different.