Steering Assist Control Solenoid Return Circuit Low (GM)
The C0503 code means the vehicle's onboard diagnostic system has detected: Steering Assist Control Solenoid Return Circuit Low (GM). This is a serious severity code.
- Keep driving?
- Yes, but fix soon
- DIY difficulty
- moderate
- Estimated cost
- $150 - $900 (sensor or wiring; steering assist components at the high end)
Basic scanners cannot read ABS codes. BlueDriver reads all systems including ABS, SRS, and transmission through your phone.
Basic scanners cannot read ABS codes. This one reads all four systems so you know exactly which sensor failed.
Affiliate links — we earn a commission at no extra cost to you.
Common Symptoms
- Steering effort wrong - too heavy or overly light
- Warning light or message on
- Assist may vary with speed incorrectly
Probable Causes (Ranked by Likelihood)
- Fault in the power steering assist component this code names (Steering Assist Control Solenoid Return Circuit Low) High
- Damaged wiring or a corroded connector in that circuit - road-splash zones corrode connectors High
- Failed related sensor or actuator Moderate
- Control module fault Low
Frequently Asked Questions
What does C0503 mean?
C0503 is a chassis code used primarily by GM vehicles: Steering Assist Control Solenoid Return Circuit Low. It concerns the power steering assist system.
Can I keep driving with C0503?
Generally yes; the power steering assist system may be degraded. Diagnose soon, and treat any brake- or steering-related behavior change as urgent.
Is C0503 the same on every make?
The decimal C0xxx range is dominated by GM's assignments (Chevrolet, GMC, Buick, Cadillac). Other makes may use this ID differently - if your vehicle is not a GM product, verify the meaning in your make's service information.
Mechanics Guide Step-by-step diagnosis
Step-by-Step Diagnostic Procedure
-
Read the code with a GM-capable scan tool and note the symptom byte/subcode if shown.
-
View live data for the named circuit (e.g. all four wheel speeds while rolling for wheel-speed codes).
-
Inspect the circuit's wiring and connectors - chassis harnesses live in the splash zone and corrode first.
-
Follow the GM pinpoint test for C0503 before replacing components.
Sources 1
This page is built from documented references. Verify against your own service info before repair work.
- SAE J2012Diagnostic Trouble Code Definitions (defines the generic OBD-II code ranges)
Commonly Affected Vehicles
- Chevrolet, GMC, Buick, Cadillac (GM chassis code range)
Related Codes
Explore More
Was this helpful?
Send this to whoever is fixing the car — your mechanic, or the person asking what the light means.