C0550 Code: Electronic Control Unit Performance (Internal Fault)
A GM chassis module, most often the brake module (EBCM), failed its own internal self-check.
Safety first · Consult a professional
- Braking system affected: ABS may be disabled. Drive carefully and have it checked promptly.
At a glance
Severity: Moderate
- Meaning
- Electronic Control Unit Performance (Internal Fault)
- System
- Brakes, ABS & Chassis · Chassis
- Safe to drive?
- With caution
- Typical repair cost
- $50–$1,600
- DIY difficulty
- Hard
C0550 is GM's 'ECU performance' code: the module that stored it has found a problem with itself, such as a memory checksum error, a processor watchdog fault or missing programming. It's most often logged by the EBCM, but GM also uses it in electric power steering, electronic parking brake and transfer case modules, so the first job is to see which module reported it. The symptom byte narrows it down; for example -45 or -46 point to program or calibration memory, -49 to an internal electronic failure and -51 to a module that isn't programmed. Before condemning the module, rule out unstable power and ground, because voltage dips can corrupt the self-test.
Can I keep driving? If the brake module stored it, normal brakes work but ABS and stability control are off, so drive gently. If the power steering module stored it and steering is heavy, drive only as far as necessary and at low speed.
How to read C0550
- C Chassis
- 0 Generic (SAE)
- 5 Brakes, ABS & Chassis
- 50 Specific fault
Symptoms
- ABS, traction and StabiliTrak warnings together
- Heavy steering and a power steering warning if the steering module is affected
- Parking brake or 4WD warning if those modules stored the code
- Scan tool can read the module but some data values are missing
- Problem started after a battery replacement, jump-start or module swap
Possible causes
Ranked by how often each cause is behind this code (editorial estimate).
- Internal hardware failure in the module (memory, processor or circuit board)
- Voltage dips or a poor ground corrupting the module's self-test
- Replacement or used module not programmed or configured for the vehicle
- Water intrusion or corrosion on the module or its connector
- Software fault that a programming update corrects
- Voltage spike from welding, reversed jumper cables or faulty accessories
Diagnosis step by step
Find out which module stored it
Run a full-vehicle scan. C0550 in the EBCM, the power steering module and the parking brake module lead to different repairs, so note the module name and symptom byte before anything else.
Tools: OBD-II scanner
Check battery and charging health
Test the battery with a load tester and check that charging voltage stays around 13.5-14.7 V. A battery that dips below about 9.5 V on cranking can make modules log internal faults.
Tools: Multimeter
Measure module power and ground under load
Back-probe the module's battery feed and ground pins with the key on and the system working. Feeds should be within about 0.5 V of battery voltage and grounds should show less than 0.2 V drop.
Tools: Multimeter
Inspect for water and corrosion
Unplug the module and inspect pins and seals. Modules mounted low near the wheel wells or on the frame are prone to water entry, especially after winters with road salt.
Tools: Screwdriver, Flashlight
Clear and retest
Clear codes, cycle the key off for a couple of minutes so the module fully sleeps, and restart. A C0550 that returns immediately with good power and ground confirms an internal fault.
Tools: OBD-II scanner
Program or replace
If the byte indicates programming or a known software issue, a dealer-level reprogram may fix it. Otherwise replace or rebuild the module, then program it and run any required setup, such as steering angle calibration or brake bleeding.
Tools: OBD-II scanner
Where the parts are
- 1Battery
- 2Alternator
- 3Engine computer (ECM)
- 4CAN bus
- 5Transmission
- 6Wheel speed sensor
- 7High-voltage battery
Repair options & costs
| Repair | DIY? | Estimated cost |
|---|---|---|
| Repair module power or ground | Yes | $50–$200 |
| Replace battery | Yes | $150–$320 |
| Reprogram or update module software | No | $100–$250 |
| Rebuild EBCM (mail-in) | Yes | $150–$450 |
| Replace and program EBCM or power steering module | No | $500–$1,600 |
Rough US estimates for parts and labor; shop rates vary by region. Not a quote.
Notes by brand
Field data
| Chevrolet | 3 | Malibu Maxx, Cobalt |
|---|
Source: NHTSA Complaints API (US government open data), analyzed by DTC mention.
Emissions / smog test impact
Depends
C0550 isn't part of an OBD emissions test. A state safety inspection may fail the vehicle if ABS, stability or power steering warnings stay on.
Frequently asked questions
Does C0550 always mean I need a new brake module?
No. Low battery voltage, bad grounds and missing programming can all set it. Replace the module only after power, ground and software have been ruled out.
Why does C0550 appear in the power steering module?
GM uses the same generic 'ECU performance' code across many chassis modules. In the steering module it means that module failed its self-check, which can remove power assist.
Can a used EBCM from a junkyard fix it?
Only if it's the right part and it's programmed for your vehicle. A used module that isn't set up often stores C0550 with a 'not programmed' byte straight away.
Why do I also see C0561?
C0561 is a follow-up code that records that the stability system was disabled. Once the C0550 cause is repaired, C0561 usually clears as well.
Sources
- Manufacturer public service information (cross-checked)
- NHTSA Complaints API
- Methodology: How We Build Code Pages · Data Sources We Use · Editorial Policy