CAT Engine 22466 Fault Code: Engine Glow Plug Relay : Current Above Normal
Also called Glow Plug Start Aid Relay : Current Above Normal, Glow Plug Start Aid Relay Current Above Normal, Glow Plug Start Aid Relay current above normal
Engine Glow Plug Relay : Current Above Normal · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
CAT code 22466 (SPN 676 / FMI 6) means the ECM has detected a high current, short circuit condition in the glow plug start aid relay circuit while the engine is not cranking. The ECM cannot control the relay, so glow plugs may not operate at all or may run continuously, causing hard cold starts and possible white exhaust smoke.
Medium severity. This code does not stop the engine from running, but it disables proper cold start assistance and can leave glow plugs powered continuously, which risks premature relay or glow plug failure and hard starting in cold weather. Diagnose before the next cold start if possible.
What does CAT Engine error code 22466 mean?
CAT code 22466, SPN 676 FMI 6, points to the glow plug start aid relay circuit reading a current level higher than the ECM expects, which it interprets as a short circuit. This is a current-above-normal fault, not a temperature or sensor fault, so the issue lives in the wiring, connectors, relay, or glow plugs themselves rather than in engine operating conditions.
The glow plug starting aid exists to help the engine start when cold. The ECM watches coolant temperature and intake manifold air temperature, and if conditions call for it, activates the start aid relay for a controlled period, feeding power to the glow plugs. Some machines pair this with a Wait to Start lamp that tells the operator to hold off cranking while the glow plugs do their work.
When this fault sets, the ECM can no longer control the relay properly. Depending on the failure, glow plugs may stop working entirely or may stay powered all the time. Either way, expect harder cold starts and possibly white smoke at startup since the engine is not getting the intended preheat assistance.
What triggers a CAT Engine 22466 code?
The ECM sets this code when the engine is not cranking, the ECM has been powered for at least 1 second (some versions state 2 seconds), and a high current or short circuit condition is present in the glow plug start aid relay circuit for more than 2 seconds. If the ECM was previously blank (no prior codes logged), it requires a total of 2 hours of operation before this diagnostic code will actually be logged.
Common causes of 22466
- Damaged, corroded, or chafed connectors and wiring in the glow plug start aid relay circuit
- A problem within the wiring harness itself, including a short circuit between the fuse and the glow plug start aid relay
- Blown fuses in the glow plug start aid circuit
- An intermittent electrical problem that only shows up under certain conditions
- A faulty glow plug start aid relay, including a fault in the relay coil
- A faulty or shorted glow plug
- A bad or faulty ECM
- A fault in the wiring specifically between the relay and the ECM
How to troubleshoot CAT Engine 22466: first checks
- Inspect all connectors and wiring associated with the glow plug start aid relay circuit for corrosion, chafing, pinched wires, or damaged pins
- Check the fuses feeding the glow plug start aid circuit and confirm they have not blown
- Test the glow plug start aid relay itself, including checking the relay coil for a short, and swap with a known-good relay if available
- Check individual glow plugs for a short to ground or internal failure
- Trace the wiring between the relay and the ECM specifically, since a short in this run is a documented cause
- Look for signs of intermittent connection issues by wiggling harness connectors while monitoring for the fault, since intermittent problems are a listed cause
- If all wiring, relay, and glow plugs check good, suspect the ECM itself
How the code clears
No separate clearing step is listed beyond fixing the underlying short circuit or component fault. Once the damaged wiring, connector, relay, or glow plug is repaired or replaced, the code should stop being logged on subsequent cold start attempts. Keep in mind that if the ECM was previously blank of codes, it takes a total of 2 hours of engine operation before this code will log again, so a short test run may not immediately confirm a repair.
Frequently asked questions
What does CAT code 22466 mean?
It means the ECM detected a high current, short circuit condition in the glow plug start aid relay circuit while the engine was not cranking. This is SPN 676, FMI 6, a current-above-normal fault.
Will code 22466 stop my engine from running?
No, this fault affects the glow plug starting aid, not core engine operation. However, it can cause hard cold starts, white exhaust smoke on startup, and it may leave glow plugs powered all the time, which risks damaging the relay or plugs over time.
Why is my engine hard to start in cold weather with this code active?
Because the ECM cannot properly control the glow plug start aid relay, the glow plugs either fail to operate or run continuously instead of cycling on a controlled schedule, so the intended cold-start preheat assist is not working correctly.
What is the Wait to Start lamp and does it relate to this code?
The Wait to Start lamp, where installed, illuminates to tell the operator the glow plugs are actively preheating before cranking. With code 22466 active, this feature may not function correctly since the ECM cannot properly activate the relay.
How long does it take for this code to log on a new or reset ECM?
If the ECM was previously blank of codes, it requires a total of 2 hours of engine operation before this diagnostic code will be logged, even if the short circuit condition is present.
What parts are most commonly responsible for this fault?
Damaged wiring or connectors, a faulty glow plug start aid relay including a shorted relay coil, a faulty glow plug, or a short between the fuse and the relay are the most commonly cited causes. A bad ECM is possible but less common.