C0045 on 2018 GMC Sierra 2500: Causes and Fixes for Left Rear Wheel Speed Sensor Circuit

What's Unique About the 2018-2018 Gmc SIERRA 2500

For 2018 GM HD trucks, the C0045 code is specifically addressed in a Technical Service Bulletin (TSB). GM issued TSB #PIE0456A as an engineering inquiry to gather data on vehicles reporting various warning lights related to the ABS and StabiliTrak systems, accompanied by codes C0045 or C0050. This indicates that GM is aware of a pattern of potential issues in the wheel speed sensor circuits on these specific trucks, often related to the sensor itself, the wiring harness connectors, or the harness routing along the axle and frame.

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 illuminated
• Service StabiliTrak / Traction Control warning light on
• Service Trailer Brake System message displayed
🎬 Watch: How to fix these common dashboard warning lights.
• Brake pedal feels different or makes a grinding/dragging noise at low speeds as the ABS system incorrectly activates

Most Likely Causes

1. Faulty Left Rear Wheel Speed Sensor 🔴 High Probability The sensor is an electronic component exposed to harsh conditions (water, salt, debris) and can fail internally. GM has acknowledged issues with these circuits on this platform via TSB PIE0456A. 🎬 Watch: Why these specific codes trigger on GM trucks. A YouTube video on a 2017 Sierra 2500 HD shows this exact replacement.
   How to confirm: Use a scan tool to monitor live data for all four wheel speed sensors while driving. If the left rear sensor shows 0 MPH or an erratic reading while the others read correctly, the sensor is the primary suspect. The sensor can be tested with a multimeter for resistance; it should be between 850-1350 ohms when disconnected.
   Typical fix: Replace the left rear wheel speed sensor. It is sold as a sensor and pigtail harness assembly and is held in by a single 8mm or T30 Torx bolt.
   Est. part cost: $40-$90
2. Damaged Wiring or Connector 🟡 Medium Probability The wiring harness leading from the sensor along the axle tube and up to the frame is susceptible to damage. Common failure points include chafing against the frame or suspension components, and corrosion inside the main connector on the frame rail. Sometimes, rust buildup under the sensor's mounting point ('rust jacking') can physically push the sensor slightly out of alignment, increasing the air gap to the tone ring and causing an intermittent signal.
   How to confirm: Visually inspect the entire wiring harness from the sensor to the main loom on the frame. Unplug both the sensor-side connector and the frame-rail connector and check for green/white corrosion, bent pins, or water intrusion. Check for continuity on both wires in the harness from end to end.
   Typical fix: Repair the broken wire(s) or replace the pigtail connector. If rust jacking is present, remove the sensor and thoroughly clean the mounting surface on the hub down to bare metal before reinstalling. Ensure the harness is properly secured in all its clips away from moving parts.
   Est. part cost: $20-$50
3. Damaged Wheel Hub/Bearing Assembly ⚪ Low Probability The magnetic reluctor ring (encoder) that the sensor reads is integrated into the wheel hub. Contamination with metallic debris from a failing bearing can stick to the magnetic ring and disrupt the sensor's reading. Cracks in the ring or excessive play in the bearing can also cause an erratic signal.
   How to confirm: After removing the sensor, inspect the magnetic encoder ring on the hub. It should be a clean, uniform surface. Check for metallic 'fuzz' or debris stuck to the ring. Also, check for any side-to-side play in the wheel bearing by grabbing the tire at the top and bottom and trying to rock it.
   Typical fix: Replace the entire wheel hub and bearing assembly. This is more expensive and labor-intensive, so it should be confirmed after ruling out the sensor and wiring.
   Est. part cost: $150-$350

Rare But Worth Checking

• Faulty Electronic Brake Control Module (EBCM): This is very rare and should only be considered after the sensor, wiring, and hub have been definitively ruled out. An EBCM failure usually triggers multiple, often unrelated, codes, not just a single wheel speed sensor fault.

Diagnosis Steps

1. Connect a professional scan tool capable of reading ABS/chassis codes and live data.
2. Confirm C0045 is the active or stored code.
3. View the live data stream for all four wheel speed sensors.
4. Drive the vehicle slowly (above 5 MPH) and observe the readings. The left rear sensor should match the others. If it reads 0, is erratic, or lags, proceed with inspection.
🎬 See this walkthrough of a left rear sensor replacement.
5. Lift the rear of the vehicle and secure it on jack stands. The rear wheel does not necessarily need to be removed for access on these trucks.
6. Visually inspect the wheel speed sensor and its wiring harness for any obvious damage, such as chafing, breaks, or loose connections. Follow the harness from the hub, along the axle, and up to the frame rail.
7. Unplug the sensor and the main harness connector. Inspect all terminals for corrosion, moisture, or damage.
8. If wiring looks good, remove the single bolt (often an 8mm hex head or T30 Torx) holding the sensor in the hub assembly.
9. Gently twist and pull the sensor out. It may be stuck. Be careful not to break it off in the hub.
10. While the sensor is removed, inspect the magnetic encoder ring on the wheel hub for metallic debris or visible damage. Clean the mounting surface thoroughly.
11. If a new sensor does not fix the issue, perform a continuity test on the harness from the wheel end to the EBCM connector to rule out a hidden wire break.

Parts You'll Likely Need

• Rear Wheel Speed Sensor (OEM #23299335) — This is the most frequent point of failure for a C0045 code. It is an electronic component exposed to the elements. This part number fits both left and right rear positions.
  Trusted brands: ACDelco (GM Genuine), Delphi, Dorman, Standard Motor Products (SMP)
  OEM price range: $30-$60
  Aftermarket price range: $25-$50
• Rear Wheel Hub and Bearing Assembly — Required if the integrated magnetic encoder ring is damaged or if the wheel bearing has failed, causing excessive movement or metallic debris contamination.
  Trusted brands: ACDelco, Timken, MOOG, SKF
  OEM price range: $250-$400
  Aftermarket price range: $150-$300

Related Codes That Often Appear With This One

• C0050 — This is the code for the Right Rear Wheel Speed Sensor Circuit. Both rear sensors are mentioned in TSB #PIE0456A, share a similar wiring path, and are exposed to the same conditions. It's not uncommon for them to have similar issues or for a wiring problem to affect both circuits.

Technical Service Bulletins (TSBs) & Recalls

• PIE0456A: Service Stabilitak, ABS, Service Trailer Brake Light, and/or Service Traction Control Indicator Illuminated with DTC C0045 or C0050 Set. This was an 'Engineering Information' bulletin to gather data, not a recall.

Platform-Specific Known Issues

• A GM Technical Service Bulletin (TSB #PIE0456A) was issued for 2018 Sierra HD models for this exact code (along with C0050), indicating a known pattern of faults in the wheel speed sensor circuits that cause ABS, StabiliTrak, and trailer brake system warnings.
• The wiring harness is routed along the rear axle and can be prone to chafing or damage from road debris. The main connector on the frame rail is also a common spot for moisture and corrosion to develop, causing an open or shorted circuit.
• 'Rust jacking' under the sensor's mounting flange can increase the air gap between the sensor and the tone ring, leading to an intermittent or lost signal, a common issue in rust-belt vehicles.

Mechanic-Grade Diagnostic Values

• Wheel Speed Sensor AC Voltage Output — expected: >100mV AC, increasing with wheel speed. Failure: A reading of 0V AC indicates a dead sensor or open circuit. A fluctuating or erratic voltage that doesn't correspond to wheel speed indicates a damaged tone ring or wiring issue.
• Left Rear WSS Circuit to EBCM Connector X1 — expected: Continuity (less than 1 ohm) on both wires between the sensor pigtail and the EBCM connector pins. No continuity to ground on either wire.. Failure: High resistance or an open circuit (OL) indicates a wire break. Any continuity to ground indicates a short.

Hidden / Shadow Codes Worth Checking

• C0045 0F: Erratic Signal. This points towards a wiring issue, a poor connection, or a damaged tone ring on the hub rather than a completely failed sensor. (see via GM GDS2 or other high-end professional scan tool capable of reading manufacturer-specific symptom bytes.)
• C0045 00: No Signal / Circuit Malfunction. This typically indicates a dead sensor, a complete wire break, or a disconnected plug. (see via GM GDS2 or other high-end professional scan tool.)
• C0045 5A: Signal Plausibility Failure. The EBCM is receiving a signal, but it doesn't logically match the signals from the other wheel speed sensors. This often points to a damaged or contaminated tone ring, or excessive wheel bearing play. (see via GM GDS2 or other high-end professional scan tool.)
• C0045 18: Signal Amplitude Less Than Minimum. The signal from the sensor is too weak. This is a classic symptom of 'rust jacking,' where rust buildup has increased the air gap between the sensor and the tone ring. (see via GM GDS2 or other high-end professional scan tool.)

Scan Tool Commands That Help

• GDS2 (GM Dealer Software): ABS Data Display — This is the primary diagnostic step. It allows for real-time graphing of all four wheel speed sensors simultaneously while driving. A faulty sensor or circuit will show up as a flat line, erratic signal, or a line that doesn't match the other three sensors.

Wiring & Ground Locations

• G103 — On the outside of the left frame rail, in the engine compartment, near the radiator.. This is a primary ground for the Electronic Brake Control Module (EBCM). While a fault here would likely cause multiple ABS/StabiliTrak codes, a loose or corroded connection could potentially cause intermittent issues with a single circuit first.
• X411 — The main 16-pin chassis harness connector located on the left frame rail, roughly above the rear axle.. This is the intermediate connector between the rear axle harness (including the WSS) and the main body harness going to the EBCM. It is a very common location for water intrusion and pin corrosion, which can cause an open or short in the left rear WSS circuit.
• EBCM Connector X1, Pins 34 & 35 — At the Electronic Brake Control Module, which is attached to the ABS hydraulic block on the left frame rail.. These are the specific pins for the Left Rear Wheel Speed Sensor circuit. Pin 34 is typically the signal wire (Dark Green) and Pin 35 is the low reference (Tan/White). Testing for signal, voltage, and continuity should be done at these pins to confirm if the fault is in the wiring or the EBCM itself.

Real Owner Repair Stories

• GM-Trucks.com forum user (2017 GMC Sierra 2500HD) — ABS and StabiliTrak lights on, code C0045.
  ❌ Tried (didn't work) Replaced the left rear wheel speed sensor.
  ✅ What actually fixed it Found a chafed wire in the harness about 12 inches from the sensor plug. The harness was rubbing against the axle housing. The wire was repaired and the harness was secured with zip ties, which resolved the code.
• Diesel Place forum user (2018 Chevy Silverado 2500HD) — Service StabiliTrak message, C0045 and C0050 codes appearing intermittently.
  ❌ Tried (didn't work) Replacing both rear wheel speed sensors.
  ✅ What actually fixed it The problem was corrosion inside the main chassis connector on the frame rail (X411). The mechanic disconnected it, cleaned the green corrosion from the pins using a terminal cleaning tool, and applied dielectric grease before reconnecting. The codes did not return.
• YouTube video by a professional mechanic (2018 GMC Sierra) — ABS light on, C0045 stored.
  ❌ Tried (didn't work) Visual inspection of the sensor showed no issues.
  ✅ What actually fixed it The plastic clips holding the sensor harness to the frame had broken, allowing the harness to sag and rub against the parking brake cable. This wore through the insulation and caused an intermittent short. Repairing the two wires and properly securing the harness with new clips fixed the problem.

When the Usual Fixes Don't Work

• Multiple owner reports confirm that replacing the C0045 sensor is often not the final fix. In many cases, particularly on trucks with higher mileage or those used in harsh climates, the root cause is a failure in the wiring harness. Technicians report that a 'pin-drag' test on the frame rail connector (X411) and a thorough inspection of the harness for chafing near the axle and parking brake cable are critical steps that should be performed even before ordering a new sensor.

OEM Part Supersession History

• 22775301, 23492815 → 23299335 — Standard part revision for improved durability, weather sealing, or change in manufacturer.
  Heads up: No known incompatibilities. The newer part number is a direct, backward-compatible replacement for the older numbers on this vehicle.