C0042 on 2016-2020 Ram 2500: Brake Pedal Sensor Causes and Fixes

What's Unique About the 2016-2020 Ram 2500

Ram has specifically addressed this code in Technical Service Bulletins (TSBs). TSB S1808000152 directly points to 'Brake Pedal Missing Calibration' (C0042-54) as a known issue, especially after a PCM replacement or software flash. Furthermore, TSB 9003530 links this code to symptoms like brake lights staying on or cruise control not setting, confirming the real-world impact. The repair absolutely requires a dealer-level scan tool (wiTech) or an advanced DIY tool (like AlfaOBD or a capable Autel/Snap-on scanner) to perform the mandatory 'Brake Pedal Calibration' procedure, which is a common point of failure for DIY repairs where this 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 fourth generation (2016-2018) and the fifth generation (2019-2020) Ram 2500. The underlying cause, involving the brake pedal position sensor and its calibration, appears to be consistent across both generations. The same OEM part number (68078700AE) is listed for Ram 2500/3500 models from 2017-2021, indicating a shared component.

Symptoms You May Notice

• ABS warning light is on
• Electronic Stability Control (ESC) or Traction Control light is on
• Cruise control cannot be set or is inoperative
• Brake lights are stuck on, even when the pedal is not pressed
• Brake lights do not turn on when the pedal is pressed
• Vehicle may start without the brake pedal being pressed

Most Likely Causes

1. Brake Pedal Position Sensor Needs Calibration 🔴 High Probability → Shop Brake Pedal Calibration can be lost after a battery replacement, disconnecting the battery, or replacing the sensor or ABS/PCM module without performing the relearn procedure. TSB S1808000152 specifically identifies 'Missing Calibration' (C0042-54) as a known problem that can occur after service.
   How to confirm: Use a compatible scan tool (like wiTech or AlfaOBD) to access the ABS module and check for the specific sub-code C0042-54. Attempt to run the 'Brake Pedal Calibration' procedure. If it passes and the code clears, this was the issue.
   Typical fix: Perform the 'Brake Pedal Calibration' using a capable scan tool. This procedure is found in the ABS module's special functions and teaches the module the sensor's resting 'home' position. The pedal must not be touched during the process.
   Est. part cost: $0
2. Faulty Brake Pedal Position Sensor (BPPS) 🔴 High Probability → Shop Brake Pedal The sensor is an electronic component that can fail over time due to internal wear or electrical faults, leading to an incorrect, erratic, or nonexistent signal.
   How to confirm: If the calibration procedure fails or the code returns immediately, the sensor is likely faulty. Live data on a scan tool may show voltage that is stuck (e.g., at 5V), does not change smoothly when the pedal is pressed, or is absent entirely. A user on RamForum.com noted that an aftermarket sensor failed to work correctly, while an OEM Mopar part resolved the issue, highlighting the importance of using quality parts.
   Typical fix: Replace the Brake Pedal Position Sensor located on the brake pedal assembly. It is typically removed by a simple twist-and-pull motion. After replacement, the new sensor MUST be calibrated using a scan tool.
   Est. part cost: $40-$60
3. Damaged Wiring or Connector ⚪ Low Probability The wiring and connector are located in the driver's footwell and can be susceptible to damage from physical stress (kicking), moisture intrusion, or improper probing during previous diagnostics, which can break the delicate internal wire strands.
   How to confirm: Visually inspect the sensor's connector and wiring harness for signs of damage, corrosion, or loose pins. A technician in a YouTube video found the 5V reference wire was internally broken from previous diagnostic probing. 🎬 See this technician's walkthrough for diagnosing broken sensor wiring Use a multimeter to check for the correct 5V reference, ground, and signal continuity back to the ABS module. On a 2018 Ram 3500, the pins at the ABS module were identified as Pin 29 (5V feed), Pin 14 (return/ground), and Pin 11 (signal).
   Typical fix: Repair the damaged section of the wiring harness or replace the connector pigtail. Ensure all connections are secure and protected. In one documented case, a technician had to source a pigtail from a salvage yard due to unavailability.
   Est. part cost: $15-$50

Rare But Worth Checking

• Faulty ABS Control Module: → Shop ABS Control Module This is rare and should only be considered after a new OEM sensor, verified wiring, and proper calibration fail to resolve the code. A diagnostic video for a 2018 Ram 3500 concluded the ABS module was at fault after all other steps failed, though this is an uncommon outcome. Diagnostic procedures list this as the final step if the DTC remains active after sensor replacement.
• Improper Sensor Installation: A technician working on a Dodge Charger with the same code found that a previous mechanic had installed the sensor with the actuator arm on the wrong side of the pedal's stopper tab. This held the sensor at a constant 5V, 🎬 Watch: How to avoid common sensor installation mistakes triggering a code. While a different vehicle, the principle applies, confirming the sensor must be installed in the correct physical orientation.

Diagnosis Steps

1. Connect a professional-level scan tool (like wiTech, AlfaOBD, Autel) capable of communicating with the ABS module.
2. Read the specific C0042 sub-code (e.g., -54, -11, -2A) and any other stored DTCs.
3. If C0042-54 ('Missing Calibration') is present, navigate to the ABS module's 'Miscellaneous Functions' or 'Special Functions' menu.
4. Select and run the 'Brake Pedal Calibration' procedure, ensuring the brake pedal is not touched during the process. The procedure should only take a few seconds and report 'Pass' or 'Completed'.
5. Clear all codes and test drive the vehicle. If the code does not return, the fix is complete.
6. If the code returns, or if the calibration fails, the sensor is the next likely culprit. Use the scan tool's live data to monitor the Brake Pedal Position Sensor voltage while pressing the pedal. It should sweep smoothly (e.g., ~0.5V to ~4.5V). If it's stuck, erratic, or shows no reading, the sensor is bad.
7. Replace the Brake Pedal Position Sensor. It is located on the brake pedal support and is removed with a simple counter-clockwise twist.
8. After installing the new sensor, you MUST repeat the 'Brake Pedal Calibration' procedure. This step is not optional.
9. If the code still persists, perform a detailed inspection of the sensor's wiring and connector for damage, corrosion, or poor connection. Check for 5V supply, ground, and signal continuity from the connector to the ABS module.
10. As a final step if all else fails, diagnosis of the ABS control module itself may be necessary, though this is the least likely cause.

Parts You'll Likely Need

• Brake Pedal Position Sensor (OEM #68078700AE) — This sensor is the most common point of failure for code C0042, either through internal fault or loss of calibration memory. Replacement followed by calibration is the most frequent repair. This part number supersedes 68078700AB, 68078700AC, and 68078700AD.
  Trusted brands: Mopar
  OEM price range: $40-$60
  Aftermarket price range: $25-$45

Related Codes That Often Appear With This One

• P057B — This code for 'Brake Pedal Position Sensor Circuit Performance' is often triggered alongside C0042, as they both relate to the same sensor system. TSB S1808000152 lists them together as a known issue after PCM service.
• P1572 — This code for 'Brake Pedal Stuck' can be set when the sensor's signal doesn't change as expected, which is a condition monitored alongside the C0042 fault. TSB S1808000152 also lists this code.
• P0572 — This code for 'Brake Switch 'A' Circuit Low' is mentioned in TSB 9003530 as being related to C0042 and can cause similar symptoms like inoperative cruise control.

Technical Service Bulletins (TSBs) & Recalls

• S1808000152: Mentions C0042-54 Brake Pedal Missing Calibration, particularly after PCM service. Also lists related codes P057B and P1572.
• 9003530: Connects C0042 with brake light/cruise control issues and advises checking the Brake Pedal Home Position setting with a wiTech tool.

Platform-Specific Known Issues

• TSB #S1808000152 explicitly notes that code C0042-54 ('Brake Pedal Missing Calibration') can occur after certain service procedures like a PCM replacement, indicating a known software or procedural sensitivity on these trucks.
• TSB #9003530 confirms that for vehicles with code C0042, mechanics should use the wiTech scan tool to check the 'Brake Pedal Home Position setting', highlighting the need for specific diagnostic equipment.
• Owner experiences on forums like RamForum.com consistently point to calibration as the solution, often after a shop or owner replaces the switch but fails to perform the electronic relearn, resulting in the problem persisting.

Mechanic-Grade Diagnostic Values

• Brake Pedal Position Sensor (BPPS) Signal Voltage — expected: A smooth sweep from approximately 0.5V (pedal released) to 4.5V (pedal fully depressed) when viewed on scan tool live data.. Failure: Voltage is stuck at 0V or 5V, jumps erratically, or does not change when the pedal is pressed.
• BPPS Circuit Test at ABS Module Connector (2018 HD Example) — expected: Key On, Engine Off: Pin 29 = 5V reference feed; Pin 14 = Good ground (low resistance to chassis ground); Pin 11 = Signal voltage that varies with pedal position.. Failure: Missing 5V on Pin 29, high resistance or voltage present on Pin 14, or a static/absent signal on Pin 11 points to a wiring or module fault.
• BPPS Circuit Continuity — expected: Less than 5.0 Ohms of resistance on the signal, supply, and return wires between the sensor connector and the ABS module connector.. Failure: Resistance above 5.0 Ohms indicates an open or high-resistance fault in the wiring harness.

Hidden / Shadow Codes Worth Checking

• C0042-54: Brake Pedal Missing Calibration. This is the most common sub-code and indicates the sensor's home position is not learned by the ABS module. (see via Most professional scan tools that can access the ABS module, including AlfaOBD and wiTech.)
• C0042-11: Brake Pedal Position Sensor Circuit Short To Ground. (see via Professional scan tool capable of reading manufacturer-specific ABS codes.)
• C0042-12: Brake Pedal Position Sensor Circuit Short To Battery. (see via Professional scan tool capable of reading manufacturer-specific ABS codes.)
• C0042-62: Brake Pedal Position Sensor - Signal Compare Failure. Set when the ABS module detects brake pressure but does not see a corresponding change in the sensor's voltage signal. (see via Professional scan tool capable of reading manufacturer-specific ABS codes.)
• C0042-2F: Brake Pedal Position Sensor Circuit - Signal Erratic. The signal is intermittent or unstable. (see via Professional scan tool capable of reading manufacturer-specific ABS codes.)

Scan Tool Commands That Help

• AlfaOBD: Brake Pedal Calibration — Mandatory after replacing the BPPS, disconnecting the battery, or if code C0042-54 is present. Found by connecting to the ABS module, selecting the 'car with hood popped' icon, and choosing the procedure.
• wiTECH (Dealer Tool): Brake Pedal Position Sensor Learn / Brake Pedal Calibration — The official dealer procedure for calibrating the sensor. It is located in the ABS module's 'Miscellaneous Functions' or 'Functional Tests' menu.
• High-End Aftermarket (Autel, Snap-on): Brake Pedal Calibration / Initialization — These tools typically replicate the OEM function and can be used to perform the mandatory calibration after sensor replacement. The exact menu path may vary.

Wiring & Ground Locations

• BPPS Connector — On the brake pedal support assembly in the driver's side footwell.. This is the primary connection point for the sensor. It is susceptible to physical damage, moisture, and damage from improper diagnostic probing, which can break the internal wire strands.
• ABS Module Connector — Typically located in the engine bay, often on the driver's side. On HD trucks, removing the fender liner may be required for access.. This is the termination point for the BPPS circuit. Testing at pins 11 (Signal), 14 (Return/Ground), and 29 (5V Feed) can definitively rule out or confirm a wiring issue between the sensor and the module.
• Intermediate Harness Connector — Under the dash, between the BPPS and the firewall pass-through. A large, multi-wire connector can contain the BPPS circuit wires.. In one documented case, the locking tab on this connector was broken, causing an intermittent connection that was difficult to diagnose as checks at the sensor and module appeared normal at times.
• G101 — On the left front (driver's side) area of the engine bay, located low on the frame/body.. This is a primary ground point that supplies the ABS module. A poor connection here can cause various ABS faults, potentially including communication or sensor reference issues.

Real Owner Repair Stories

• BoostedMotorsports (YouTube) (4th Gen Ram 1500 (similar system)) — 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 OEM Mopar part.
  ✅ 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, which immediately resolved the issue.
• 3T's Mobile Automotive Repair (YouTube) (2018 Ram 3500) — C0042 code active, calibration procedure would report 'pass' but the code would immediately return.
  ❌ Tried (didn't work) A previous shop had replaced the sensor., Running the calibration routine multiple times.
  ✅ 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. The mechanic sourced a pigtail from a salvage yard, repaired the wiring, and then the calibration completed successfully and cleared the code.
• Dallas Auto Diag (YouTube) (2018 Dodge Charger (similar system)) — No start, multiple ABS codes, C0042-12 (Short to Battery), brake lights stuck on.
  ❌ Tried (didn't work) The owner had replaced the sensor with an aftermarket part.
  ✅ What actually fixed it The aftermarket sensor was installed incorrectly. The actuator arm was on the wrong side of the pedal's stopper tab, holding the sensor at its maximum reading (~5V) constantly. Reinstalling the sensor in the correct physical orientation fixed the problem.

"I Checked Everything" — The Actual Cause

• A common failure pattern for C0042 is not a failed smoke test, but a failed 'parts swap'. A technician or owner replaces the sensor, but the code immediately returns. They then suspect the new sensor or the ABS module. The actual cause is the failure to perform the mandatory 'Brake Pedal Calibration' with a capable scan tool after installation.
• In a documented case, the scan tool would report that the 'Brake Pedal Calibration' procedure passed, yet the C0042-54 code would remain active. This misleading result was caused by a damaged sensor pigtail with an internally broken wire, which was only found after thorough wiring tests.

OEM Part Supersession History

• 68078700AB, 68078700AC, 68078700AD → 68078700AE — Standard part revision and improvement by the manufacturer.
  Heads up: While no direct incompatibilities are noted between revisions, forum and video evidence strongly suggests that using OEM Mopar sensors is critical. Some aftermarket sensors have been reported to fail out of the box or be unable to calibrate correctly.

Model Year Variations Within This Range

• 2019-2020: On the 5th generation Ram, there is no longer a simple, separate on/off brake light switch. The Brake Pedal Position Sensor (BPPS) provides a variable signal directly to the ABS module, which then interprets the data and communicates the brake status to the BCM and other modules over the CAN bus to activate the brake lights.
• 2019: A small number of 2019 Ram 2500 trucks were recalled for an insecure master cylinder pushrod clip. If this clip dislodges, the brake pedal can become completely disconnected from the master cylinder, resulting in total brake failure. While this won't cause a C0042 code, it is a critical, pedal-related safety issue specific to this model year.