C0055 on 2007-2013 Cadillac Escalade EXT: Rear Speed Sensor Circuit Faults and Fixes

What's Unique About the 2007-2013 Cadillac ESCALADE EXT

The GMT900 platform, which includes the 2007-2013 Escalade EXT, is known for a specific mechanical issue that triggers the C0055 code. Manufacturer Technical Service Bulletin (TSB) PIP4966B highlights that technicians should check for "excess movement of the tone wheel or output shaft." This means that even if the sensor and wiring are good, a mechanical failure within the transfer case or transmission—often a worn rear output shaft bushing—can cause the tone ring (reluctor wheel) to wobble. This wobble creates an erratic signal that the EBCM interprets as a fault, typically setting a C0055 5A code. Additionally, the wiring harness for this sensor is known to chafe and short out where it runs over the transmission bellhousing, between the engine and firewall.

Diagnostic Flowchart

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

Symptoms You May Notice

• Service Anti-Lock Brake System message in the Driver Information Center
• Service StabiliTrak message
• ABS warning light is on
• Traction control light is on
• Cruise control may be disabled
• Erratic or harsh automatic transmission shifting
• Speedometer may twitch or read incorrectly
🎬 See how an erratic speedometer and shifting issues are diagnosed.

Most Likely Causes

1. Excessive Movement of the Rear Tone Wheel / Reluctor Ring 🔴 High Probability As documented in TSB PIP4966B, mechanical wear of the rear output shaft bushing (e.g., GM Part #19168733) in the transfer case or transmission allows the output shaft to develop excessive play. This causes the tone ring to wobble, sometimes even making physical contact with the sensor, generating an erratic signal.
   How to confirm: With the vehicle safely supported, remove the rear speed sensor. Visually inspect the tone ring for damage or runout while an assistant slowly rotates the driveshaft. Grasp the output yoke and attempt to move it up-and-down and side-to-side. Any significant play indicates a worn bushing or bearing.
   Typical fix: This is an advanced repair that involves removing the driveshaft and disassembling the transfer case or transmission tail housing to press out the old bushing and install a new one. The output shaft seal is typically replaced at the same time. 🎬 Watch: How to replace the output shaft seal and bushing.
   Est. part cost: $10-$150
2. Damaged Wiring or Connector 🔴 High Probability The wiring harness for the VSS is a very common failure point. It runs from the sensor up over the transmission bellhousing, where it is prone to chafing against the firewall/back of the engine, causing wires to short or break. This is a well-documented failure point in owner forums and repair videos for GMT900 trucks.
   How to confirm: Visually inspect the wiring harness from the sensor connector up to the main loom, paying extremely close attention to the area over the transmission. Check for melted or rubbed-through insulation. Perform a continuity test on the wires from the sensor connector to the EBCM and check for shorts to power/ground, as suggested by TSB PIT4815C.
   Typical fix: Repair the damaged section of wiring using weatherproof butt connectors and heat shrink. In some cases, a new connector pigtail is required. Some owners build a new, slightly longer harness section to bypass the damaged area completely.
   Est. part cost: $15-$50
3. Faulty Rear Wheel Speed Sensor (VSS) 🟡 Medium Probability → Shop ABS Wheel Speed Sensor The sensor is an electronic component that can fail from heat cycles and exposure to the elements. It is often replaced first, but frequently is not the root cause due to the high probability of wiring or mechanical issues.
   How to confirm: Use a scan tool to monitor the rear wheel speed data; look for dropouts or erratic readings. The sensor's resistance can be tested with a multimeter; typical values are between 1,300 and 1,426 ohms, though some sources state a wider range up to 2,900 ohms is acceptable. You can also test for AC voltage output while spinning the driveshaft.
   Typical fix: Replace the rear wheel speed sensor. It is held in by a single bolt (often 13mm or 19mm head) on the transfer case or transmission housing. The new sensor should include a new O-ring; lubricate it with transmission fluid before installation. 🎬 Watch: Step-by-step guide to replacing the rear speed sensor.
   Est. part cost: $25-$80

Rare But Worth Checking

• Faulty Electronic Brake Control Module (EBCM): → Shop ABS Control Module This is a rare cause. The EBCM is the computer that controls the ABS. It should only be considered after all other possibilities (sensor, tone ring, wiring) have been thoroughly ruled out.
• Metal Debris on Sensor Tip: The VSS is magnetic and can attract metallic particles from normal driveline wear. A significant accumulation can disrupt the signal. Remove the sensor and wipe the tip clean. If large metal chunks are present, it could indicate a more severe internal transmission or transfer case problem.

Diagnosis Steps

1. Read the trouble codes with a scanner capable of accessing the ABS module. Note if C0055 is present with a symptom byte: '00' for a circuit fault (likely wiring) or '5A' for an implausible signal (likely a loose tone ring or failing sensor).
2. Visually inspect the VSS wiring harness from the sensor connector up and over the transmission to the firewall. Look for obvious signs of chafing, melting, or corrosion. This is a critical step.
3. Use a scan tool to observe the live data from the rear wheel speed sensor while driving or spinning the rear wheels. Look for erratic signals, dropouts, or a complete lack of a signal.
4. If the signal is faulty, remove the sensor (one bolt). Inspect the magnetic tip for excessive metal debris.
5. With the sensor removed, inspect the tone ring. Check for excessive up/down/side-to-side play in the output shaft yoke, as highlighted in TSB PIP4966B. This is the most important vehicle-specific step.
6. If no mechanical play is found, test the sensor. Check resistance between the two pins; it should be within 1,300-1,426 ohms. Alternatively, check for AC voltage generation while spinning the driveshaft.
7. If the sensor tests good, perform a continuity and short-to-ground/power test on the wiring harness from the sensor connector to the EBCM connector, as suggested by TSB PIT4815C.
8. If the sensor, wiring, and tone ring/shaft are all confirmed to be good, the EBCM may be the issue, but this is the least likely cause.

Parts You'll Likely Need

• Rear Wheel Speed Sensor / Vehicle Speed Sensor (VSS) (OEM #20938122) — This sensor is a common failure point and is relatively easy to replace if it is the root cause.
  Trusted brands: ACDelco, Delphi, Bosch
  OEM price range: $50-$90
  Aftermarket price range: $25-$60
• Transfer Case Output Shaft Bushing (OEM #19168733) — Wear of this internal component is a primary cause of the 'excessive movement' of the tone ring mentioned in TSB PIP4966B. Replacing it is necessary to solve the root mechanical problem.
  Trusted brands: ACDelco, Timken
  OEM price range: $10-$40
  Aftermarket price range: $10-$30
• VSS Connector Pigtail — If the connector at the sensor is damaged or the wiring is chafed close to the connector, replacing the pigtail is the most effective repair.
  Trusted brands: ACDelco, Dorman, Standard Motor Products
  OEM price range: $25-$50
  Aftermarket price range: $15-$30

Related Codes That Often Appear With This One

• P2771 — This code for 'Four-Wheel Drive (4WD) Low Switch Circuit' is mentioned alongside C0055 in TSB PIP4966B, suggesting they can be triggered by related transfer case issues or wiring problems in the same harness area.

Technical Service Bulletins (TSBs) & Recalls

• PIP4966B: Notes that C0055 can be caused by excess movement of the tone wheel or output shaft, a key diagnostic clue for this platform pointing to a worn internal bushing.
• PIT4815C: Provides diagnostic guidance for testing the VSS circuit (circuit 817) when C0055 is the only code present, which helps differentiate a wiring/sensor issue from other system faults.

Platform-Specific Known Issues

• TSB PIP4966B specifically calls out checking for 'excess movement of the tone wheel or output shaft' as a cause for code C0055, pointing to an underlying mechanical issue (worn output bushing) in the driveline rather than just a simple sensor failure.
• The VSS wiring harness is commonly damaged where it runs over the top of the transmission, between the engine and firewall. This chafing is a well-documented failure point in owner forums and repair videos for GMT900 trucks.

Mechanic-Grade Diagnostic Values

• Vehicle Speed Sensor (VSS) internal resistance — expected: 1300-1426 ohms. Failure: An Open Loop (OL) reading or resistance significantly outside the expected range.
• VSS AC Signal Output (Raw) — expected: Approx. 1.0 VAC at 100 RPM, increasing with speed. Failure: No voltage or erratic voltage when rotating the driveshaft.

Hidden / Shadow Codes Worth Checking

• C0055 00: Indicates the EBCM has detected a circuit fault, such as an open, a short to ground, or a short to voltage. This often points to a wiring issue. (see via A professional scan tool capable of reading GM-specific ABS codes and symptom bytes, like a Tech2 or high-end Autel/Snap-on scanner.)
• C0055 5A: Indicates the EBCM has detected an erratic or implausible signal. This often points to a failing sensor or a mechanical issue like a loose tone ring. (see via A professional scan tool capable of reading GM-specific ABS codes and symptom bytes, like a Tech2 or high-end Autel/Snap-on scanner.)

Wiring & Ground Locations

• EBCM (Electronic Brake Control Module) — Mounted on the left rear frame rail.. This module receives the rear wheel speed signal. Tests for the VSS circuit will terminate at this module's connector. The VSS signal is on circuit 817, as mentioned in TSB PIT4815C.
• G103 / G104 — Grounds located on the engine cylinder heads (G103 often on the front, G104 on the rear passenger side). These are primary engine and component grounds.. A poor engine ground can introduce electrical noise or cause voltage drops that may affect sensor readings, although it's a less common cause for a specific C0055 code.
• VSS Harness Chafe Point — The wiring harness runs up from the transfer case/transmission and over the top of the bellhousing, between the back of the engine and the firewall.. This is the most common location for the VSS wiring to rub through, causing shorts or open circuits that directly trigger code C0055.

Real Owner Repair Stories

• YouTube channel 'Repairs and Stuff' (2007-2013 era GMC/Chevy Truck (GMT900 platform)) — Speedometer twitching and erratic shifting, along with ABS/Stabilitrak lights and code C0055.
  ❌ Tried (didn't work) Replacing the Vehicle Speed Sensor (VSS) on the transfer case.
  ✅ What actually fixed it The wiring harness that runs over the top of the transmission had chafed through. The final fix was to repair the broken wires in that harness section.
• DuramaxDiesels.com forum user (GM Truck with C0055) — ABS light and C0055 code, jumpy/jerky feeling only at steady speeds between 50-55 mph.
  ❌ Tried (didn't work) Initial diagnosis focused only on the sensor.
  ✅ What actually fixed it The user identified play in the transfer case output yoke and confirmed with others that a worn output shaft bushing was the likely cause of the erratic signal, requiring bushing replacement to fix the mechanical wobble that triggers the code.

OEM Part Supersession History

• 15121067, 20763147 → 20938122 — Part has been updated by the manufacturer.
  Heads up: The newest part number, 20938122, is the correct service replacement for the entire 2007-2013 model range.
• 88984505 → 19168733 — Part has been updated by the manufacturer.
  Heads up: 19168733 is the correct service replacement bushing for the transfer case output shaft.

Model Year Variations Within This Range

• 2007-2013: The core causes for C0055 (worn bushing, chafed harness, failed sensor) are consistent across the 2007-2013 Escalade EXT model years. No significant design changes to the VSS, its wiring path, or the transfer case output assembly have been noted that would alter the diagnostic approach. All years use a single rear VSS on the AWD transfer case.