C0045 on 2008-2014 Mercedes-Benz C-Class: Left Rear Wheel Speed Sensor Circuit Fixes

What's Unique About the 2008-2014 Mercedes-Benz C-Class

The 2008-2014 C-Class (W204 chassis) relies heavily on accurate wheel speed data for its ABS and ESP systems. While a failed sensor is a common cause for the C0045 code on any car, the W204 is particularly susceptible to corrosion and damage of the rear reluctor ring (also called a tone ring). This ring is pressed onto the axle shaft, and over time, rust can build up underneath it, causing it to swell, crack, or break entirely. This expansion changes the air gap to the sensor or presents a damaged surface, leading to erratic signals. Many owners report that simply replacing the sensor does not fix the issue, and the reluctor ring must also be inspected and often replaced.

Symptoms You May Notice

• ABS warning light illuminated
• ESP (Electronic Stability Program) or Traction Control warning light illuminated
• "Run Flat Indicator inoperative" me 🎬 Watch: Fix the run flat indicator error by replacing the sensorssage on the dashboard
• Cruise control may be disabled
• ECO start/stop system may be inoperative
• In rare cases, the power steering may feel heavy if the fault is related to a failing ABS module
• Brake pedal may feel different or pulsate unexpectedly at low speeds if the system is trying to activate based on faulty data

Most Likely Causes

1. Corroded or Damaged Reluctor Ring 🔴 High Probability The metal reluctor ring (or tone ring) is press-fit onto the rear axle shaft. It is exposed to the elements, and rust commonly forms between the ring and the shaft. This rust buildup causes the ring to expand, leading to cracks or complete breakage, which generates an incorrect signal for the sensor. This is a very well-documented and frequent failure point on the W204 platform.
   How to confirm: After removing the ABS sensor, visually inspect the reluctor ring on the axle shaft through the sensor mounting hole. Use a light and a small mirror if necessary. Look for visible cracks, missing teeth, heavy rust buildup, or any signs of deformation or swelling. A cracked or delaminated ring is definitive proof. 🎬 See this video showing a failed rear ABS sensor ring
   Typical fix: The old, damaged ring must be carefully broken off the axle shaft with a chisel. The shaft surface is then thoroughly cleaned of all rust and scale with a wire wheel or sandpaper. A new reluctor ring is then carefully pressed or tapped into place. This is often done at the same time as sensor replacement.
   Est. part cost: $20-$50
2. Failed Left Rear Wheel Speed (ABS) Sensor 🔴 High Probability → Shop ABS Wheel Speed Sensor The sensor is located in the wheel well, where it is constantly exposed to water, road salt, and debris. This can lead to internal electronic failure or corrosion of its connector pins over time.
   How to confirm: Use a diagnostic scan tool with live data capability to monitor the wheel speed from the left rear sensor while driving or spinning the wheel. If it reads 0 mph or shows an erratic signal while the other three wheels report speed accurately, the sensor is likely faulty. You can also test the sensor's internal resistance with a multimeter and compare it to the manufacturer's specification (typically 500–1500 Ω for passive sensors). W204 sensors are active sensors, and a simple resistance test may be misleading; checking for a voltage signal while spinning the wheel is more reliable.
   Typical fix: Replace the left rear ABS sensor. This involves removing the wheel, disconnecting the sensor's electrical plug, and removing a single bolt (usually an E-Torx or Allen head) 🎬 Watch: Step-by-step W204 ABS sensor replacement DIY holding it to the wheel carrier.
   Est. part cost: $40-$150
3. Wiring Harness or Connector Damage 🟡 Medium Probability The wiring harness runs from the ABS module down to the wheel hub and is susceptible to damage from road debris, improper jacking/servicing, or chafing against suspension components. The connector itself can also become filled with dirt or water, causing corrosion on the pins.
   How to confirm: Visually inspect the entire length of the sensor's wiring from the sensor itself to where it enters the cabin/chassis. Pay close attention to areas where it bends or is secured by clips. Unplug the connector and check for green or white corrosion on the pins. Perform a continuity test with a multimeter from the sensor connector to the ABS module connector to check for opens or shorts in the circuit.
   Typical fix: Repair the broken or shorted section of wire using solder and heat shrink tubing. If the connector is corroded, it should be cleaned with electrical contact cleaner or replaced entirely.
   Est. part cost: $10-$50

Rare But Worth Checking

• Faulty ABS Control Module: → Shop ABS Control Module This is the least likely cause and should only be considered after the sensor, reluctor ring, and wiring have all been confirmed to be in good condition. A failing module often triggers other codes related to internal faults or communication errors, such as 5001, 5944, or 5945. Diagnosis requires a high-level scanner to check module communication status.
• Worn Wheel Bearing: A severely worn wheel bearing can cause excessive play in the hub. This movement can alter the gap between the sensor and the reluctor ring, leading to an erratic or lost signal. This is usually accompanied by a humming or grinding noise from the corner of the vehicle that changes with speed.

Diagnosis Steps

1. Connect a Mercedes-compatible OBD-II scanner (like a STAR/Xentry or advanced aftermarket tool) to confirm the C0045 code and check for any other stored codes.
2. Access the live data stream for the ABS/ESP module.
3. Drive the vehicle slowly (or raise the rear and spin the wheel by hand) and observe the wheel speed readings for all four wheels. Confirm that the Left Rear (LR) wheel speed is reading 0, is erratic, or significantly differs from the other three.
4. Raise and safely support the rear of the vehicle on jack stands. Remove the left rear wheel.
5. Visually inspect the ABS sensor wiring and connector for any obvious damage, corrosion, or chafing.
6. Disconnect the sensor and remove the single bolt (often an E8 or E10 Torx) holding it to the wheel carrier.
7. With the sensor removed, use a flashlight to carefully inspect the reluctor ring on the axle shaft through the sensor hole. Look for cracks, heavy rust, or warping. A cracked ring is a very common failure.
8. If the ring is damaged, it must be replaced. This involves chiseling off the old ring, cleaning the axle shaft surface meticulously, and pressing on a new one.
9. If the ring appears intact, the sensor is the next most likely culprit. Test the old sensor's signal with an oscilloscope or by checking for voltage output while spinning the wheel. A simple resistance test on these active sensors can be misleading.
10. If a new sensor and ring do not solve the issue, perform a continuity and resistance check on the wiring harness between the sensor connector and the main ABS control module to rule out a wiring fault.

Parts You'll Likely Need

• Rear ABS Wheel Speed Sensor (OEM #A2045400317, A2049050100, 2049057900) — This is a common component to fail in the circuit due to its exposed location and electronic nature. Part numbers can supersede, so verifying with VIN is recommended.
  Trusted brands: Bosch, ATE, Delphi, VEMO, Continental
  OEM price range: $100-$150
  Aftermarket price range: $40-$80
• Rear ABS Reluctor Ring (Tone Ring) (OEM #A2303570182) — This part is highly prone to corrosion and cracking on the W204 platform, which causes an incorrect signal even with a new sensor. This part number is widely cited for this application.
  Trusted brands: Febi Bilstein, Meyle, AIC
  OEM price range: $30-$50
  Aftermarket price range: $20-$40

Related Codes That Often Appear With This One

• 5001, 5944, 5945 — These are Mercedes-specific codes indicating an internal fault within the ABS/ESP control unit. If you see these along with C0045, it points towards a potential ABS module failure rather than just a sensor issue.
• 5130 — This is a Mercedes-specific code that may appear on some scanners, such as the Launch CRP123, which directly translates to a fault with a rear axle RPM sensor.

Platform-Specific Known Issues

• A well-documented issue on W204 forums is the failure of the rear reluctor rings due to rust buildup on the axle shaft, which cracks the ring. Many owners recommend inspecting or replacing the ring whenever a rear speed sensor fault occurs.
• The reluctor ring has 96 teeth (magnetic segments) and is magnetic, not a traditional toothed ring. Aftermarket rings are available with anti-corrosion coatings to prolong their life.

Documented NHTSA Reports

While C0045 is a standard wheel speed sensor code, cross-manufacturer records highlight common failure points. For instance, NHTSA ODI #11219167 describes a case where the left rear wheel speed sensor encoder ring was broken, requiring replacement of both the sensor and the hub assembly. Similarly, NHTSA ODI #11165895 notes that a service center reported code C0045 and recommended replacing the hub bearing assembly to resolve intermittent stability control messages. In some electronic systems, this code can even appear alongside unrelated faults; NHTSA ODI #11399819 reports C0045 appearing in conjunction with fuel level sensor codes P0463 and P069E, while NHTSA ODI #10382746 notes it appearing with several other chassis codes (C0057, C0231, C0232, C0282) which required a software re-program.

Mechanic-Grade Diagnostic Values

• Active Wheel Speed Sensor Voltage Supply — expected: 5V or 12V DC. Failure: Missing reference voltage points to a wiring or ABS module issue.
• Active Wheel Speed Sensor Signal Output — expected: Pulsing DC square wave (viewable on an oscilloscope) as the wheel spins.. Failure: A missing or erratic signal, when supply voltage is present, indicates a failed sensor.
• Passive Wheel Speed Sensor Resistance (for general reference, though W204 uses active sensors) — expected: Typically 800 - 1700 Ω, but can vary by manufacturer.. Failure: An open circuit (infinite resistance) or a short circuit (zero resistance) indicates a failed sensor.

Hidden / Shadow Codes Worth Checking

• 5130: L6/4 (Right rear axle RPM sensor) or equivalent for Left rear. This is a manufacturer-specific code that directly points to the wheel speed sensor circuit. (see via Advanced scanners like Launch or the dealer-level STAR/Xentry system.)

Scan Tool Commands That Help

• iSCAN (or equivalent high-level tool like Xentry): ESP Module Coding, VIN Write, and Teach-in Adaptations — This is required if the ABS/ESP control module itself is replaced. The module must be coded to the vehicle, have the VIN written to it, and have adaptations performed for successful commissioning. This can be done on new or compatible used modules.
• Launch CRP123 (or equivalent): Clear Fault Memory — After replacing the faulty component (sensor or ring), the stored fault code must be cleared from the ABS/ESP module to extinguish the warning lights. On the W204, the lights may not clear automatically just by driving.

Wiring & Ground Locations

• N30/4 (ESP Control Unit) — Located in the front left of the engine compartment, attached to the hydraulic unit.. This is the module that receives the signal from the left rear wheel speed sensor. All wiring for the sensor ultimately terminates here.
• ESP Control Unit Connector Pins 36 & 37 — At the main connector for the N30/4 ESP control unit.. Pin 36 is for the signal from the rear left wheel sensor (Blue/White wire), and Pin 37 is the return/power (Red/White wire). These pins can be used for continuity testing of the harness from the module to the sensor.
• Front SAM (Signal Acquisition Module) Fuses — Fuse box located in the engine compartment on the driver's side.. The ABS/ESP module is powered by several fuses in the front SAM. Specifically, fuses F14, F20, and F35 have been identified as being related to the ABS module and should be checked if there are power-related issues.

Real Owner Repair Stories

• Reddit user in r/w204 (Mercedes-Benz W204 (year not specified)) — ABS, ESP, tyre pressure, cruise control, and start/stop error lights all illuminated.
  ❌ Tried (didn't work) Replacing the rear wheel speed sensor.
  ✅ What actually fixed it The actual cause was the reluctor ring (ABS ring/tone ring). The user replaced the ring, which resolved all the warning lights. The repair took about 2 hours.
• YouTube channel 'Parknest' (2009 Mercedes-Benz W204 C200) — ABS/ESP warning lights. A scan revealed a fault related to the 'left rear axle' signal component.
  ❌ Tried (didn't work) The owner had previously fixed the same issue on the right side, so they went straight for the suspected cause.
  ✅ What actually fixed it Replacing the left rear ABS reluctor ring. Upon removal, the old ring was found to be delaminated and 'absolutely crusty'. After cleaning the CV joint surface and fitting the new ring, the codes were cleared and the issue was resolved.
• MBClub UK forum user (2011 W204 C200 CDI, 50k miles) — ESP/ABS inoperative warning.
  ❌ Tried (didn't work) A new sensor was fitted to the left rear, but the fault persisted., The user then swapped the known-good sensor from the right side to the left, and the fault still remained on the left side, seemingly ruling out the sensor itself.
  ✅ What actually fixed it The user fitted the *old* working sensor from the right side onto the left rear, and the fault cleared. This indicated that the brand new sensor they had purchased was either Dead on Arrival (DOA) or had a bad contact pin. The reluctor ring was not the cause in this specific, unusual case.

OEM Part Supersession History

• A2045400317 → A2049050100 — Standard part number evolution by the manufacturer.
  Heads up: The parts are generally interchangeable for the W204 rear axle, but it is always best practice to confirm fitment with the vehicle's VIN.

Model Year Variations Within This Range

• 2012-2014 (Facelift): The W204 received a major facelift for the 2012 model year, which included a completely redesigned interior and updated braking system features like a 'hold' function. While the fundamental cause of C0045 (sensor/ring failure) remains the same across the generation, part numbers for control modules or software versions could differ between pre-facelift (2008-2011) and post-facelift (2012-2014) models.

Diagnostic Flowchart

Other Known Issues on This Vehicle

Issues unrelated to this code that are worth knowing about as an owner of this generation:

• Electronic Steering Lock (ESL) Failure 🔴 High — Very common, especially on pre-facelift models. Can occur without warning, preventing the car from starting.
• Rear Subframe Corrosion 🔴 High — Widespread issue, particularly in regions with road salt. Can lead to MOT/inspection failure and structural compromise. (Ref: Extended Warranty (20 years) issued by Mercedes in some regions.)
• M272 V6 Engine Balance Shaft Sprocket Wear 🔴 High — Affects V6 petrol engines (C230, C280, C300, C350) built before ~mid-2008. Failure typically occurs between 60k-100k miles. (Ref: A class-action lawsuit was filed in the US. Mercedes issued a service bulletin with affected engine serial numbers.)
• 7G-Tronic (722.9) Conductor Plate Failure 🟠 Medium — Common on pre-facelift models (before 2012) with the 7-speed automatic transmission, typically between 60k-120k miles.
• M271 Engine Timing Chain Stretch 🔴 High — Common on 4-cylinder petrol models (C180, C200, C250) from 2007-2012. Can occur as early as 60k-80k miles.

Used vs. New Parts: Buying Guide for This Vehicle

When a used part is the smart pick: For this repair, used parts are generally not recommended. The primary failure components, the ABS sensor (an electronic part) and the reluctor ring (a part that fails from corrosion), have limited lifespans. The cost of new aftermarket parts is low enough that the labor involved in installing a used part with an unknown history is not worth the risk.

Donor-vehicle mileage cap: roughly under 50000 miles for the part to have meaningful remaining life.

What to inspect on the donor part:

• If considering a used axle shaft assembly, inspect the reluctor ring for any signs of rust, swelling, or cracking before purchase.
• Verify the donor vehicle is from a dry, salt-free climate to minimize the risk of corrosion-related failure.
• Avoid used ABS sensors entirely, as they are electronic wear items with no reliable way to gauge remaining life.

OEM-only on this vehicle (don't cheap out):

• ABS Control Module (ESP Module): While used modules can be programmed, the complexity and critical safety function make a professionally remanufactured or new OEM unit the safest choice if replacement is necessary.

Aftermarket brands forum-validated for this vehicle:

• Sensors: Bosch, ATE, Hella, Vemo, Continental. Forum users and mechanics often recommend sticking to premium OE-supplier brands for sensors to avoid compatibility issues.
• Reluctor Rings: Febi Bilstein, Meyle, AIC. These are commonly available and cited as reliable replacements.

Brands owners have reported issues with on this vehicle:

• Unbranded, low-cost sensors from online marketplaces. While tempting, these have a higher rate of being Dead on Arrival (DOA) or failing prematurely, leading to repeat repairs.

Real Owner Stories

Aggregated from forums and TSBs cited above. Mileages and costs reflect what owners reported in those sources.

Related OBD-II Codes

• C0046 — Right rear wheel speed sensor fault; shares the same failure mode of reluctor ring corrosion and expansion on the W204 platform.
• C0037 — Left rear wheel speed sensor circuit fault; often triggered alongside C0045 when the sensor or wiring harness is damaged by road debris or corrosion.
• C0038 — Right rear wheel speed sensor circuit fault; related to the same axle and sensor design used across the W204, X204, and C207 platforms.

Frequently Asked Questions