C0800
Device Power #1 Circuit MalfunctionC0800 is a generic OBD-II chassis diagnostic trouble code: Device Power #1 Circuit Malfunction. It is logged by the engine control unit when the chassis monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.
What C0800 means
C0800 — Device Power #1 Circuit Malfunction — indicates that the Electronic Brake Control Module (EBCM) or another chassis-side control module has detected a voltage or current anomaly on its primary 12 V supply circuit. On GM platforms (Silverado, Tahoe, Equinox, Terrain, Acadia, and related Buick/Cadillac variants) this circuit is fed from the main underhood fuse block through a dedicated relay; the EBCM monitors the supply continuously and logs C0800 when voltage falls below the operating threshold or the feed is momentarily lost.
The most common real-world trigger is a voltage sag during engine cranking. If the battery is weak, a corroded positive cable, or a high-resistance ground strap allows the supply to drop too low while the starter is engaged, the EBCM resets and stores C0800. This manifests as an intermittent ABS warning lamp that appears and clears on its own — often only after cold starts or after the vehicle sits for several days. The E411 chassis harness connector (on Equinox and Terrain) is a known corrosion hotspot in the EBCM power feed path.
C0800 shares the same root-cause family as B1983 (control module voltage out of range) and P2509 (ECM/PCM power input signal intermittent). Diagnosing it requires measuring actual voltage at the EBCM fuse and connector under load — static voltage checks with the engine idling are insufficient and will miss intermittent sags during cranking.
Common causes
Most-frequently reported root causes when C0800 is logged.
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1
Weak or partially discharged battery causing voltage to drop below the EBCM's minimum operating threshold during cranking.
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2
Corroded or loose positive battery cable or main ground strap creating high resistance in the EBCM supply path.
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3
Blown fuse in the EBCM power feed circuit (underhood fuse block).
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4
Failed or intermittent power relay supplying the EBCM or ABS module.
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5
Corroded E411 harness connector near the fuel tank (common on Chevrolet Equinox and GMC Terrain).
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6
Faulty alternator unable to maintain adequate charging voltage under electrical load.
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7
EBCM internal power supply fault requiring module replacement.
Symptoms drivers notice
How to diagnose C0800
A typical diagnostic flow when this code is present.
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1
Perform a battery load test (CCA test); replace battery if capacity is below 70% — this resolves the majority of C0800 occurrences.
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2
Inspect battery terminals, positive cable to fuse block, and chassis ground straps for corrosion or looseness; clean and re-torque as needed.
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3
Locate the EBCM fuse in the underhood fuse block and verify it is intact and making good contact.
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4
Measure voltage directly at the EBCM power supply connector during cranking (not just at idle); voltage should remain above approximately 9–10 V throughout the crank event.
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5
On Equinox/Terrain models, inspect the E411 connector in the rear chassis harness for green corrosion and treat with electrical contact cleaner and dielectric grease.
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6
Test the EBCM power relay for proper pull-in voltage and contact resistance.
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7
Clear the code, perform several cold-start cycles, and confirm C0800 does not return before returning the vehicle to the customer.
Related chassis codes
Frequently asked questions
Why does the ABS light come on only after cold starts and then go off by itself?
A weak battery has higher internal resistance when cold, causing a deeper voltage sag during the initial crank. Once the alternator brings voltage back up, the EBCM recovers and the light extinguishes. This intermittent pattern is the classic symptom of C0800 caused by a failing battery.
Is it safe to drive with C0800 active?
The vehicle is driveable because the base hydraulic brakes remain functional. However, ABS and stability control are disabled while the fault is present, which reduces safety in emergency braking and slippery conditions. Diagnose and repair promptly.
Will clearing the code fix the problem?
No. Clearing C0800 without fixing the underlying power supply issue will only result in the code returning, usually within a few drive cycles or the next cold start. The root cause — typically a weak battery, corroded cable, or bad relay — must be corrected first.
How is C0800 different from B1983 or P2509?
All three codes describe module supply voltage anomalies but are set by different modules: C0800 is set by the EBCM (chassis system), B1983 is typically set by the BCM or an accessory module (body system), and P2509 is set by the ECM/PCM when its own ignition run/start power input is intermittent. A weak battery or faulty alternator can trigger all three simultaneously.
Disabling C0800 in software
RaceTune can permanently disable C0800 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.
Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.
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