C0037 on 2019-2020 Ram 3500: Left Rear Wheel Speed Sensor Causes and Fixes

What's Unique About the 2019-2020 Ram 3500

On this generation of Ram 3500, particularly dual rear wheel (DRW) models, code C0037 is frequently triggered under specific conditions like towing heavy loads or driving on rough surfaces like rumble strips. Manufacturer Technical Service Bulletins (TSBs) S2205000002 and 9004400 acknowledge that this code can appear even when there are no hardware problems, sometimes pointing to a software calibration issue or stress on the wiring harness from suspension compression. TSB S2205000002 specifically advises that if diagnostics don't find a fault and the issue only happens on rough roads with a load, part replacement is not recommended as a software solution is anticipated.

Diagnostic Flowchart

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

Symptoms You May Notice

• ABS warning light is on
• Electronic Stability Control (ESC) or traction control warning light is on
• "Service 4WD System" message may appear
• "Service Trailer Brake System" message may appear, especially when towing
• Cruise control is inoperative
• ABS and traction control systems are disabled

Most Likely Causes

1. Damaged or Stretched Wiring Harness 🔴 High Probability TSBs S2205000002 and 9004400 specifically note that this code can be set while towing or hauling a heavy payload, which can stress and damage the wiring harness. A common failure point is where the harness is routed above the fuel tank; moisture can get trapped in the loom, causing wires (specifically the Dark Green/Gray wire) to corrode and break. Chafing against the frame rail or inner fender well liner is another known issue.
   How to confirm: Visually inspect the entire length of the wiring harness from the left rear wheel to the main chassis harness. Look for chafing, breaks, corrosion in the connector, or stretched wires. A diagnostic check showing ~12V at a chassis connector but a much lower voltage (e.g., 1-2V) at the sensor connector points to an open or high-resistance circuit in the harness.
   Typical fix: Repair the damaged section of wire or replace the connector pigtail. In some cases, technicians run a new twisted pair of wires to bypass a damaged section in the loom, avoiding the need to drop the fuel tank.
   Est. part cost: $15-$50
2. Faulty Left Rear Wheel Speed Sensor 🔴 High Probability → Shop ABS Wheel Speed Sensor The sensor is exposed to harsh conditions. TSB 05-004-24 notes that vibrations from driving over rumble strips can cause the sensor to send an erratic signal (C0037-2F), recommending replacement as the fix.
   How to confirm: Use a scan tool to monitor live data from all four wheel speed sensors while driving. If the left rear sensor's reading is erratic or drops to zero while the others read correctly, the sensor is likely bad. Swapping the left and right rear sensors and seeing if the code changes to C003A (right side) can also confirm a bad sensor.
   Typical fix: Replace the left rear wheel speed sensor.
   Est. part cost: $50-$160
3. Software/Calibration Issue 🟡 Medium Probability TSB 9004400 was issued for dually trucks that set this code without any detectable hardware faults, suggesting a logic or calibration issue within the ABS module under certain driving conditions. TSB S2205000002 also points to this, advising against part replacement if the issue only occurs under load on rough roads.
   How to confirm: This is a diagnosis of exclusion. If the sensor, wiring, and tone ring are all confirmed to be good, but the code persists (especially when towing), the issue is likely software-related. A user on Reddit reported their persistent C0037-1D and -2F codes were resolved after a dealer performed a recall on the ABS module.
   Typical fix: The vehicle's ABS module software needs to be updated by a Ram dealership. Check for any open recalls or software update TSBs like 08-061-20.
   Est. part cost: $0-$250
4. Debris on Sensor or Damaged Tone Ring ⚪ Low Probability As a heavy-duty truck, these vehicles may operate in muddy or dirty environments. Metallic debris from brake wear or mud can accumulate on the magnetic sensor tip or in the teeth of the tone ring, obstructing the signal.
   How to confirm: Remove the wheel speed sensor and inspect its magnetic tip for debris. Visually inspect the tone ring (located on the axle hub) for damage, rust, or packed-in debris. A cracked or severely corroded tone ring will send erratic signals.
   Typical fix: Clean the sensor tip and the tone ring with a brush and brake cleaner. If the tone ring is cracked or has broken teeth, the axle hub assembly will likely need to be replaced.
   Est. part cost: $0-$300+

Rare But Worth Checking

• Failing ABS Control Module: → Shop ABS Control Module While rare, the ABS module itself can fail. This is usually a last resort after all other components (sensor, wiring, tone ring) have been ruled out. One owner on Reddit reported their persistent C0037 issue was only resolved after the dealer replaced the ABS module at low mileage. Companies like XeMODeX offer repair services for these modules, citing wheel speed sensor codes as a common failure symptom.
• Worn Wheel Bearing/Hub Assembly: Excessive play in a worn wheel bearing can change the air gap between the sensor and the tone ring, causing an erratic signal. One owner on a forum noted this issue occurred specifically while towing, as the extra load caused the axle to deflect more, triggering the code.

Diagnosis Steps

1. Connect an ABS-capable scan tool to confirm code C0037 is present and check for any specific sub-codes (e.g., -1D, -2F).
2. Use the scan tool to view the live data stream for all four wheel speed sensors. Drive the vehicle slowly or spin the wheel by hand and compare the reading from the left rear sensor to the others. Look for dropouts or erratic behavior.
3. Perform a thorough visual inspection of the left rear wheel speed sensor's wiring harness from the wheel well up to where it joins the main loom. Pay close attention to areas near suspension components and above the fuel tank for signs of chafing, stretching, or corrosion.
4. Unplug the sensor and inspect the connector for bent, corroded, or pushed-out pins. Check for voltage at the connector; a significant drop from the expected ~12V points to a wiring issue.
5. Remove the sensor (typically held by a single bolt) and inspect its magnetic tip for metal shavings or other debris. At the same time, inspect the tone ring on the hub for damage or debris.
6. If wiring looks good, test continuity on the sensor wires (often Dark Green/Gray and Dark Green/Yellow) from the sensor connector back to the ABS module connector.
7. If the wiring and tone ring are good, and the live data was erratic, the sensor is the most likely cause. Consider swapping the left and right rear sensors to see if the code follows the sensor.
8. If all hardware checks out, especially if the code only appears when towing or hauling on a dually, consult a Ram dealer about performing a software update for the ABS module as per TSBs 9004400 and S2205000002.

Parts You'll Likely Need

• Left Rear Wheel Speed Sensor (OEM #68646345AB (supersedes 68646345AA)) — This sensor is the primary component that generates the wheel speed signal. It can fail from heat and vibration, and its replacement is the specific fix recommended by TSB 05-004-24.

Related Codes That Often Appear With This One

• C003A — This is the code for the Right Rear Wheel Speed Sensor. The TSBs often list C0037 and C003A together because the conditions that cause the fault (like towing stress or driving over rumble strips) can affect both rear wheel sensors simultaneously.
• C0037-1D — This is a sub-type of the main code meaning 'Circuit Current Out of Range'. It more specifically points towards an electrical problem like an open wire, a short circuit, or a bad connector, rather than a sensor that's just reading erratically. A YouTube video by 'Ravalli County Customs' details diagnosing this specific code on a 2020 Ram, tracing it to an open wire.
• C0037-2F — This sub-type means 'Signal Erratic'. It is specifically mentioned in TSBs related to driving over rumble strips or when towing, and can be caused by vibration, a failing sensor, or a loose connection.
• U0415 — This code means 'Invalid Data Received from ABS Control Module'. It often appears alongside a specific wheel speed sensor code because the primary fault (C0037) is causing the ABS module to send bad data to other vehicle systems, like the powertrain or transfer case control modules.

Technical Service Bulletins (TSBs) & Recalls

• 05-004-24: C0037-2F set when driving over rumble strips; recommends sensor replacement.
• S2205000002: C0037-2F set while driving with payload or towing.
• 9004400: C0037-2F on dually trucks with no hardware faults found.

Platform-Specific Known Issues

• TSB 05-004-24: Notes that the ABS and ESC lamps can illuminate after driving over rumble strips, setting code C0037-2F. The recommended repair is to replace the rear wheel speed sensor(s). The TSB lists labor times of 0.4 hours for one sensor and 0.5 for both.
• TSB S2205000002: Acknowledges that C0037-2F can be set while driving with a payload or towing on rough roads. It explicitly states that if standard diagnostics do not find a fault, part replacement is not recommended and that a solution was anticipated for late 2023, suggesting a software calibration issue.
• TSB 9004400: Specifically addresses dual rear wheel trucks setting C0037-2F or C003A-2F without any hardware problems, particularly when the customer mentions driving on highways. This points to a software logic issue under specific vibration/load conditions.

Mechanic-Grade Diagnostic Values

• Voltage at sensor connector (power wire) — expected: ~12V with key on, engine off.. Failure: A reading significantly lower than 12V (e.g., 1-2V) points to high resistance or an open in the wiring harness between the ABS module and the sensor.
• Sensor signal (on a working sensor) — expected: These are Hall-effect sensors. The voltage signal is superimposed on the power wire, typically varying by about 0.4V as the wheel spins (e.g., toggling between 11.0V and 11.4V).. Failure: A flat line or no voltage at all on the signal wire indicates a wiring or sensor issue.

Wiring & Ground Locations

• ABS Module Connector (C3) — Located in the driver's side front wheel well, attached to the Hydraulic Control Unit (HCU).. This is the termination point for the wheel speed sensor circuits. Testing for continuity and voltage here is critical for isolating a wiring fault from a module fault.
• Left Rear WSS Circuit Pins at ABS Module — At the main ABS module connector, the Left Rear Wheel Speed Sensor wires are Pin 37 (Positive, Dark Green/Gray wire) and Pin 36 (Negative, Dark Green/Yellow wire).. Knowing these specific pin numbers allows a technician to perform a continuity test on the harness from the module directly to the sensor connector, definitively proving if the wiring is intact.
• Harness Chafe Point (Above Fuel Tank) — Inside the main wiring loom where it passes over the top of the fuel tank.. This is a well-documented but hard-to-access failure point. Moisture gets trapped, causing the Dark Green/Gray wire to corrode and break, creating an open circuit that triggers C0037-1D.
• Harness Chafe Point (Front Wheel Well) — Where the main harness runs along the frame and can be rubbed by the inner fender well liner in the driver's side front wheel area.. A YouTube video documented a case where this chafe point wore through the insulation and destroyed the wires for the left rear wheel speed sensor, causing an open circuit.

Real Owner Repair Stories

• YouTube channel 'Phillip Bailey' (2016 Ram 3500 (similar wiring and issue)) — ABS and traction control lights on.
  ❌ Tried (didn't work) Initial inspection of easily accessible wiring.
  ✅ What actually fixed it The final fix was finding a corroded and broken Dark Green/Gray wire inside the harness loom where it runs above the fuel tank. A new twisted pair of wires was run to bypass the damaged section.
• YouTube channel 'Ravalli County Customs' (2020 Ram 1500 with C0037-1D (similar wiring and issue)) — ABS and traction control lights on, code C0037-1D.
  ❌ Tried (didn't work) Replacing the ABS sensor did not fix the issue.
  ✅ What actually fixed it The technician found that the driver's side front fender well liner had rubbed through the main wiring harness, severing the wires for the left rear speed sensor. The harness was repaired to fix the open circuit.
• hdrams.com forum user (2020 Ram 3500 with 30,000 miles) — ABS/ESC lights on, codes C0037-1D and C003A-1D, especially when towing.
  ❌ Tried (didn't work) Replacing both rear wheel speed sensors.
  ✅ What actually fixed it After the owner was unable to find the fault, the dealership diagnosed and found a broken wire in the harness located above the fuel tank. Repairing the wire resolved the codes.

OEM Part Supersession History

• 68646345AA → 68646345AB — Standard part revision by the manufacturer.
  Heads up: None noted. 68646345AB is a direct replacement for 68646345AA.

Model Year Variations Within This Range

• 2019-2021 vs 2022+: The infotainment system changed from Uconnect 4 to Uconnect 5 in 2022. While not directly related to the ABS system, it's a notable electronic change within the 5th generation Ram platform.