C0042 on 2015-2020 Ram 1500: Brake Pedal Position Sensor Causes and Fixes

What's Unique About the 2015-2020 Ram 1500

This issue is common enough on Ram trucks that multiple Technical Service Bulletins (TSBs) have been issued. Unlike many other vehicles where a brake switch is a simple on/off device, the Ram 1500 uses a more sensitive analog position sensor that requires electronic calibration after replacement. Simply swapping the part is often not enough to fix the problem; the ABS module must be taught 🎬 Watch: How to calibrate the sensor and fix stuck brake lights the new sensor's home position using a diagnostic tool. Many DIYers and even some shops miss this step, leading to the code returning immediately. Tools like the dealer's wiTECH or enthusiast-level software like AlfaOBD are required to perform this calibration.

Diagnostic Flowchart

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

Generation note: The 2015-2020 year range covers the end of the fourth generation Ram 1500 (DS), which ran until 2018, and the start of the fifth generation (DT), which began in 2019. The Brake Pedal Position Sensor issue and the C0042 code are documented as problems on both generations, with TSBs and owner complaints covering vehicles from 2015 through 2020. The underlying electronic architecture that requires sensor calibration is present in both generations, though the specific part number for the sensor changed between the DS and DT generations.

Symptoms You May Notice

• ABS warning light is on
• Electronic Stability Control (ESC) or traction control warning light is on
• Check Engine Light may be on
• Cruise control will not engage or disengages unexpectedly
• Brake lights stay on continuously, even when the truck is off, draining the battery
• Brake lights do not turn on when pressing the pedal
• Remote start may be disabled as a safety precaution

Most Likely Causes

1. Faulty Brake Pedal Position Sensor (BPPS) 🔴 High Probability The sensor is a known high-failure item, as evidenced by multiple TSBs and widespread owner reports. It is a sensitive electronic component that can fail internally, leading to erratic or no signal.
   How to confirm: Use a scan tool to monitor the BPPS voltage live data while pressing the pedal. A healthy sensor should show a smooth voltage change (e.g., ~0.5V to ~4.5V). If the voltage is stuck, erratic, jumps, or doesn't change, the sensor is almost certainly bad. Some owners report that aftermarket sensors are more likely to fail or be out-of-spec from the box.
   Typical fix: Replace the Brake Pedal Position Sensor with a new OEM Mopar part and perform the calibration procedure.
   Est. part cost: $20-$50
2. Lost or Missing Calibration 🔴 High Probability Calibration can be lost after replacing the battery, the sensor itself, the ABS module, or if the battery is disconnected for an extended period. TSB #S1808000152 directly calls out "Brake Pedal Missing Calibration" (C0042-54) as a cause for this code. This is the most common reason the code appears immediately after a DIY sensor replacement.
   How to confirm: Using a capable scan tool (like AlfaOBD or wiTECH), attempt to run the "Brake Pedal Calibration" or "Brake Pedal Position Sensor Learn" routine. The procedure is found in the ABS module's miscellaneous functions/functional tests. If the procedure completes successfully and the code clears (and stays cleared), this was the issue.
   Typical fix: Perform the calibration routine. The scan tool will instruct you not to touch the brake pedal during the process.
   Est. part cost: $0 (if you own a scan tool)
3. Wiring or Connector Issue 🟡 Medium Probability The wiring for the sensor is located in the driver's footwell and can be susceptible to damage from kicking, moisture from wet boots, or improper installation of aftermarket equipment like floor mats or remote starters. The connector pins can also lose tension or corrode.
   How to confirm: Visually inspect the sensor's connector and wiring harness for any signs of damage, corrosion, or loose pins. A technician in a detailed repair video noted that previous probing of the wires had broken a 5V reference wire 🎬 See a professional diagnostic walkthrough for the C0042 code internally within the harness, which was difficult to find. Check for 5V reference, ground, and a changing signal voltage at the connector with a multimeter.
   Typical fix: Repair the damaged wiring or replace the connector pigtail. In one documented case, a salvaged connector was required as a new pigtail was not readily available.
   Est. part cost: $15-$40

Rare But Worth Checking

• Faulty ABS Control Module: This is rare and should only be considered after the sensor, wiring, and calibration have been thoroughly checked and ruled out. The module is the component that reads the sensor's signal, and an internal failure can mimic a sensor problem. A failure here is expensive, so exhaustive diagnosis is key.

Diagnosis Steps

1. Connect a scan tool capable of reading ABS codes (e.g., AlfaOBD, wiTECH). Read codes from all modules, paying special attention to the ABS module. Note any related codes like P057B or P1572.
2. Using the scan tool, navigate to the ABS module's live data for the Brake Pedal Position Sensor. Observe the voltage as you press and release the brake pedal. The reading should be smooth and consistent, typically from ~0.5V to ~4.5V. Any erratic jumps, flat lines, or no change indicates a problem.
3. Inspect the sensor, its connector, and the nearby wiring harness for any physical damage, corrosion, or looseness. Check for moisture in the footwell area.
4. Attempt to perform the 'Brake Pedal Calibration' routine using the scan tool. This is usually found under 'Miscellaneous Functions 🎬 Watch: Using AlfaOBD to solve common Ram electronic problems' or 'Functional Tests' in the ABS module menu. Do not touch the brake pedal during this procedure.
5. If the calibration fails or the code immediately returns with the same sensor, the sensor is the primary suspect. If calibration passes but the code returns as 'active' or 'stored', it could point to an intermittent wiring issue.
6. Replace the Brake Pedal Position Sensor. It is located on the brake pedal support bracket and is removed with a simple counter-clockwise twist-and-lock motion.
7. After installing the new sensor, you MUST perform the 'Brake Pedal Calibration' routine again. This is not an optional step.
8. Clear all DTCs from all modules and perform a test drive. Verify that the brake lights function correctly, cruise control engages, and no ABS/ESC warning lights return.

Parts You'll Likely Need

• Brake Pedal Position Sensor (OEM #68273742AA (verify fitment, may be superseded)) — This is the component that fails most frequently, causing the C0042 code. It is the primary part identified in service bulletins and countless owner repair stories.
  Trusted brands: Mopar
  OEM price range: $20-$50
  Aftermarket price range: $15-$40

Related Codes That Often Appear With This One

• P057B — This code for 'Brake Pedal Position Sensor Circuit Performance' is often seen with C0042, as documented in TSB #S2008000192 and #S1808000152.
• P1572 — This code for 'Brake Pedal Stuck' can be triggered by the same faulty sensor data, as noted in TSB #S1808000152.
• P0572 — A generic code for 'Brake Switch 'A' Circuit Low', it points to the same component and is mentioned alongside C0042 in TSB #9003530.
• U0415 — Implausible Data Received From Anti-Lock Brake System Module. This can be set in other modules (like the PCM or BCM) when the ABS module reports bad data from the brake sensor.

Technical Service Bulletins (TSBs) & Recalls

• S2008000192: Addresses CEL and ESC lights with DTCs C0042-28 and P057B.
• S1808000152: Mentions C0042-54 (Brake Pedal Missing Calibration) along with other brake pedal sensor codes.
• 9003530: Recommends checking Brake Pedal Home Position for C0042 and related symptoms like brake lights staying on.

Platform-Specific Known Issues

• TSB #S2008000192 notes that C0042 can appear with P057B, illuminating the Check Engine and ESC lights.
• TSB #S1808000152 specifically links C0042-54 to a 'Brake Pedal Missing Calibration' condition, often after a PCM replacement or flash.
• TSB #9003530 advises technicians to check the 'Brake Pedal Home Position setting' with the wiTech scan tool for vehicles with code C0042, especially if cruise control or brake light issues are present.
• Owner experiences consistently show that using an aftermarket sensor can be problematic, with some failing to calibrate or failing prematurely. Sticking with an OEM Mopar part is highly recommended.

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 and supply circuit 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 Circuit at ABS Module (2018 Ram HD example) — expected: Pin 29: 5V reference feed. Pin 14: Ground/Return. Pin 11: Signal voltage that varies with pedal position.. Failure: Missing 5V feed, missing ground on the return line, or a static signal voltage indicates a wiring or module issue.

Hidden / Shadow Codes Worth Checking

• C0042-11: Brake Pedal Position Sensor Circuit Short to Ground. (see via Professional scan tools like wiTECH or advanced DIY tools like AlfaOBD will display this sub-code.)
• C0042-12: Brake Pedal Position Sensor Circuit Short to Battery. (see via Professional scan tools like wiTECH or advanced DIY tools like AlfaOBD will display this sub-code.)
• C0042-2A: Brake Pedal Position Sensor - Stuck. (see via Professional scan tools like wiTECH or advanced DIY tools like AlfaOBD will display this sub-code.)
• C0042-54: Brake Pedal Missing Calibration. (see via This is a common sub-code displayed by many scan tools when calibration has not been performed or was lost.)

Scan Tool Commands That Help

• AlfaOBD: Brake Pedal Calibration — This procedure is mandatory after replacing the brake pedal position sensor or disconnecting the battery for an extended period. It is found by connecting to the ABS module, selecting the 'car with hood popped' icon for procedures, and choosing 'Brake Pedal Calibration'.
• wiTECH (Dealer Tool): Brake Pedal Position Sensor Learn / Brake Pedal Calibration — Used by dealerships to perform the mandatory calibration after sensor or module replacement. The function is typically located in the ABS module's 'Miscellaneous Functions' or 'Functional Tests' menu.

Wiring & Ground Locations

• ABS Module Connector Pins (2018 HD Example) — At the main harness connector for the ABS control module.. Allows for definitive testing of the entire circuit. Pin 11 is the signal wire, Pin 14 is the sensor return (ground from module), and Pin 29 is the 5V sensor feed. Testing here can isolate a wiring fault from a sensor 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 of failure due to physical stress, moisture, or damage from probing wires. A broken wire or corroded pin here will cause the C0042 code.

Real Owner Repair Stories

• 3T's Mobile Automotive Repair (YouTube) (2018 Ram 3500) — C0042 code, calibration would not complete successfully.
  ❌ Tried (didn't work) A previous shop replaced the sensor, but the code remained., Running the calibration routine would report 'pass' but the code would immediately return as active.
  ✅ What actually fixed it The wiring pigtail to the sensor was damaged from previous diagnostic probing, causing an internal break in the 5V reference wire and a poor connection on the ground return pin. The mechanic sourced a pigtail from a salvage yard, rewired it, and then the calibration completed successfully.
• Dallas Auto Diag (YouTube) (2018 Dodge Charger (similar system)) — No start, multiple ABS communication codes, and active code C0042-12 (Short to Battery). Brake lights were stuck on.
  ❌ 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 actuator arm was on the wrong side of the pedal's stopper tab, causing the sensor to be held at its maximum reading (5V) at all times. Reinstalling the original OEM sensor in the correct physical orientation resolved the issue.
• BoostedMotorsports (YouTube) (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.
  ✅ What actually fixed it The new sensor required calibration. The owner used the AlfaOBD app on an Android tablet 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.

"I Checked Everything" — The Actual Cause

• In one documented case on a 2018 Ram 3500, the sensor had been replaced and the calibration procedure was attempted multiple times. The wiring appeared visually intact, but the code persisted. The actual cause was an internal break in the 5-volt reference wire within the harness, caused by a previous technician piercing the wire with a test probe. This type of damage is not visible externally and was only found by testing continuity from the ABS module connector to the sensor connector.

OEM Part Supersession History

• 68078700AD → 68078700AE — Standard part revision.
  Heads up: This part number series generally applies to the 4th Generation (DS) Ram 1500 (approx. 2015-2018).
• 68340480AA → 68340480AB — Standard part revision.
  Heads up: This part number series applies to the 5th Generation (DT) Ram 1500 (2019+). It is not interchangeable with the 4th Gen (DS) part.

Model Year Variations Within This Range

• 2015-2018 (4th Gen 'DS'): Uses brake pedal position sensors with part numbers like 68273742AA or 68078700AE.
• 2019-2020 (5th Gen 'DT'): Uses a different brake pedal position sensor, part number 68340480AB. While the failure mode and need for calibration are the same, the physical part is not interchangeable with the previous generation.