METERING UNIT – PREHEATER FAILURE
Indicates a failure in the preheater metering unit.
Heads up: this code wasn't in our hand-written library yet, so DiagCoach AI built this page on the fly. Double-check critical specs against service info before condemning parts.
What it means (plain English)
The preheater should help warm up the engine more quickly, but if it fails, the engine won't warm up properly and might run rough or inefficiently.
What the computer is actually seeing
The engine control module (ECM) monitors the preheater's operation by checking its input current and output temperature. If it detects that the preheater isn't operating, or it sees inconsistent signals, it triggers this fault code.
What a healthy reading looks like
Preheater current should typically be around 10-20 amps when in operation. The temperature should rise to at least 150°F within 5-10 minutes.
Guided diagnostic — the DiagCoach way
Don't just throw parts at it. Walk through these in order — each step tells you whether to keep going or stop and fix what you found.
- 1Check the wiring and connectors for the preheater. Look for signs of wear or corrosion. Do the same for the ECM connector.
- 2Inspect the fuse for the preheater circuit to ensure it is not blown. Replace if necessary.
- 3Using a multimeter, check the current going to the preheater while starting the engine. It should be around 10-20 amps. If not, there's a fault in the circuit.
- 4Test the preheater metering unit by applying direct power to it. It should activate smoothly and draw appropriate current without overheating. If it doesn’t, replace the unit.
Common causes
- Faulty preheater metering unit
- Wiring or connector issues
- Blown fuse for heater circuit
- Faulty coolant temperature sensor
Typical repair cost
$$$
Related codes
Frequently asked questions
Is it safe to drive with this code?
It's drivable, but you may notice longer warm-up times and rough engine performance.
Will this code come back after clearing?
If the underlying issue isn't fixed, the code will likely return.
Why does it pair with SPN 1112?
Both codes are related to issues with the preheater and its control circuit.
Working a real vehicle right now?
Let DiagCoach walk you through it live with your specific symptoms, vehicle, and what you've already checked.
Start guided diagnostic →