John Deere Engines SPN676FMI5 Fault Code: Cold Start Aid Circuit Has High Resistance
Also called Cold Start Aid Drive Circuit Has High Resistance, Cold Start Aid Drive Circuit has High Resistance, Glow Plug Relay Output Signal Not Received, Glow Plug Relay Voltage Low
Cold Start Aid Circuit Has High Resistance · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
SPN 676 FMI 5 sets when the John Deere ECU commands the cold start aid (glow plug) relay ON but detects the relay output is low, meaning the relay never actually energized. It's logged as a Warning and usually shows up as a stored code because the active window is brief. Left unaddressed, cold starts in low temperatures may take longer or fail.
Medium severity. This is logged as a Warning-level code. The engine will keep running and the ECU keeps controlling it in a normal manner, but cold-weather starting can suffer if the glow plug or cold start aid circuit stays inoperative, so it's worth diagnosing before the next cold start rather than ignoring it.
What does John Deere Engines error code SPN676FMI5 mean?
SPN 676 FMI 5 means the ECU sent a command to turn the cold start aid (also called the glow plug) relay ON, then checked the relay's output and found it low, effectively telling the ECU the relay never energized. The ECU uses fuel temperature or coolant temperature (depending on the platform) to decide when this relay needs to switch on, then supplies a high side control signal to the relay coil and monitors the relay's output as feedback.
Because the code only stays active for the short time the relay is commanded on, it typically shows up in the ECU's memory as a stored code rather than an active one. That doesn't mean the problem went away, it just means you may not catch it live unless you're watching during a cold start attempt.
The bigger real-world impact is on starting in cold weather. If the glow plug or cold start aid circuit isn't actually powering up when commanded, the engine may need extended crank time or may not start at all in low ambient temperatures.
Common causes of SPN676FMI5
- Blown or missing cold start aid/glow plug fuse
- Open or short circuit in the wiring harness, including an open relay control circuit or an open circuit between the relay output and the ECU
- Loose or corroded connections, including bad terminals or connector at the ECU
- Bad terminals or connector at the cold start aid/glow plug relay itself
- High resistance between the cold start aid relay control coil side terminal and single point ground
- Defective cold start aid or glow plug relay (on some platforms identified as relay K5803)
- Bad terminals or connector at connector X5004 (where applicable)
- Bad ECU software
- Bad ECU
How to troubleshoot John Deere Engines SPN676FMI5: first checks
- Check the cold start aid/glow plug fuse first: confirm it is present, not blown, and seated well in its holder.
- Inspect the wiring harness between the ECU and the cold start aid relay for open circuits, chafed insulation, or shorts, paying close attention to the relay control circuit and the relay output-to-ECU path.
- Pull the relay connector and the ECU connector and look at the terminals for corrosion, looseness, or pushed-back pins. Clean and reseat as needed.
- Check for high resistance between the relay's control coil ground side terminal and the single point ground; a poor ground connection here can mimic a bad relay.
- Test or swap the cold start aid/glow plug relay itself (on platforms where it's identified, this is relay K5803) to rule out a defective relay.
- If wiring, fuse, connectors, and the relay all check out, consider ECU software or a bad ECU as the remaining possibilities.
How the code clears
No separate clearing step is listed. Since this DTC is logged when the ECU commands the relay OFF, and the active window is brief, it typically appears as a stored code. After repairing the fuse, wiring, connector, or relay issue, run the engine through a cold start aid activation cycle (cold weather conditions or a Harness Diagnostic Mode Test on the platform that supports it) to confirm the fault does not recur, then clear the stored code with your diagnostic tool.
Frequently asked questions
What does SPN 676 FMI 5 mean on a John Deere engine?
It means the ECU commanded the cold start aid or glow plug relay to turn on, then detected that the relay's output was low, so the relay never actually energized. It's logged as a Warning-level code.
Will my John Deere engine still run with this code active?
Yes. The ECU continues to control the engine in a normal manner. The main risk is with cold starting: the engine may need extended crank time or may fail to start in low ambient temperatures if the glow plugs or cold start aid aren't powered.
Why does this code only show up as stored and not active?
The fault condition is only checked during the brief window when the ECU is commanding the relay on. Once the ECU commands the relay off, the code moves from active to stored, so you may only see it in stored history unless you catch it during a cold start attempt.
What's the most common cause of SPN 676 FMI 5?
Fuse and wiring issues are the most commonly listed causes: a blown or missing cold start aid/glow plug fuse, an open or short in the harness, or loose/corroded connections at the ECU or relay connector. A defective relay is also a frequent cause.
Is SPN 676 FMI 5 the same as SPN 676 FMI 6?
No, they're related but distinct. FMI 6 points to a low current fault detected on the cold start aid drive circuit itself, which can occur when ignition is on and the cold start aid activates, including during a Harness Diagnostic Mode Test. FMI 5 specifically means the relay output was low when the ECU commanded it on.
Can a bad ground cause this code?
Yes. High resistance between the cold start aid relay's control coil side terminal and the single point ground is listed as a possible cause, and it can produce symptoms similar to a failed relay.
Do I need a scan tool to diagnose this code?
A scan tool capable of reading John Deere ECU diagnostic trouble codes is needed to confirm the code and, on supported platforms, to run a Harness Diagnostic Mode Test that can help isolate wiring versus relay versus ECU causes.