CAT Engine 1680 Fault Code: System Voltage High
Also called Electrical System Voltage : High, Electrical System Voltage High
System Voltage High · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
CAT code 1680, also logged as CID 168-FMI 00 or flash code 51, means the ECM has detected battery supply voltage above 32 VDC (or above 16 VDC on 12-volt systems) for a set time while the keyswitch is ON and the engine is not cranking. It points to a charging system or wiring problem that can damage the ECM if not corrected.
High severity. Sustained overvoltage can damage the ECM and other electronics. The code is treated as a warning condition rather than an immediate shutdown, but it should be diagnosed before continued operation.
What does CAT Engine error code 1680 mean?
Code 1680 (SPN 168, FMI 0) fires when the engine ECM sees battery voltage that is too high for its rated 12-volt or 24-volt system. The ECM continuously monitors unswitched battery voltage supplied through dedicated pins, and when that voltage climbs above its threshold for the specified time, the ECM logs the fault and may light a warning lamp.
This is fundamentally a charging system and wiring health check. The ECM needs stable voltage to operate correctly and to protect its internal circuits. Persistent overvoltage, from a bad regulator, bad batteries, or wiring faults, can degrade or destroy the ECM over time.
Different OEM documentation bodies describe slightly different trigger windows and durations for this same code family, but all agree on the core condition: voltage too high, key on, engine not cranking, ECM already powered up.
What triggers a CAT Engine 1680 code?
The ECM sets this code when it reads battery supply voltage above 32 VDC for 0.5 seconds (one version states 2 seconds), the ECM has been powered for at least 3 seconds, and the engine is not being cranked. One version further requires the engine to have been running for more than 30 seconds before the code logs. On 12-volt systems, the equivalent threshold is voltage above 16 VDC for 0.5 seconds.
Common causes of 1680
- Abrasion, pinch points, or physical damage in the wiring harness between the batteries and the ECM
- Open circuit or excessive resistance in wiring or connections between the batteries and the ECM
- Damaged or corroded connectors at the ECM connector J1/P1
- Faulty, weak, or damaged batteries that need to be recharged or replaced
- Short or open in the keyswitch signal wire (wire 308-YL) between the keyswitch and the ECM
- Voltage not present on terminal B or terminal R of the keyswitch, indicating a keyswitch circuit fault or the need to replace the keyswitch
- Blown fuse or circuit breaker for the keyswitch or engine ECM circuit
- Intermittent wiring or connector problem that only shows up under vibration or load
- Faulty ECM that needs to be replaced
How to troubleshoot CAT Engine 1680: first checks
- Check battery voltage at rest and with the engine running, and compare against the 32 VDC (or 16 VDC on 12-volt systems) threshold that triggers this code
- Inspect all wiring and connectors between the batteries and the ECM connector J1/P1 for abrasion, pinch points, corrosion, or looseness
- Check continuity of the keyswitch signal wire (308-YL) between the keyswitch and the ECM for shorts or opens
- Verify voltage is present on terminal B of the keyswitch; if not, check the circuit breaker and wiring between +Battery and the keyswitch
- With voltage present on terminal B, check for voltage on terminal R; if missing, plan to replace the keyswitch
- Inspect and test the batteries themselves for state of charge and internal faults, recharging or replacing as needed
- Check the fuse or circuit breaker protecting the keyswitch and ECM power circuits for damage
How the code clears
No separate clearing step is listed beyond correcting the underlying voltage or wiring fault. The ECM logs the code automatically once the triggering condition is detected; once battery voltage, wiring, and the keyswitch circuit are repaired and voltage stays within normal range, the code should stop being active. Use a diagnostic scan tool to confirm the code clears after repair.
Affected models and serial ranges
1680 appears in our records across 6 CAT Engine models. Match your machine by model and serial number.
| Model | Serial ranges |
|---|---|
| C11 | Serial range not listed in source records |
| C13 | Serial range not listed in source records |
| C15 | Serial range not listed in source records |
| C175 | Serial range not listed in source records |
| C27 | Serial range not listed in source records |
| C32 | Serial range not listed in source records |
Frequently asked questions
What does CAT fault code 1680 mean?
It means the engine ECM detected battery supply voltage above 32 VDC (or above 16 VDC on 12-volt systems) for a short set time while the key was on and the engine was not cranking. It is an overvoltage warning for the electrical system feeding the ECM.
Is code 1680 the same as SPN 168 FMI 0 or flash code 51?
Yes. CAT displays this same condition as CID 168-FMI 00 on the Cat Data Link, as SPN 168-FMI 00 on the J1939 data link, and as flash code 51 on the diagnostic lamp.
Can I keep running the machine with this code active?
It is not an automatic shutdown, but sustained overvoltage can damage the ECM. It should be diagnosed and corrected promptly rather than ignored.
What usually causes high voltage at the ECM?
Common causes include damaged or corroded wiring and connectors between the batteries and ECM, faulty or overcharging batteries, a bad keyswitch circuit, or an intermittent connection problem. In rare cases the ECM itself may be faulty.
Where do I start troubleshooting code 1680?
Start by checking actual battery voltage against the 32 VDC or 16 VDC thresholds, then inspect wiring and connectors between the batteries and the ECM connector J1/P1, and check the keyswitch circuit wiring and terminals for proper voltage.
Does the keyswitch have anything to do with this code?
Yes. The ECM needs the keyswitch in the ON position to power up and communicate with a diagnostic scan tool. A faulty keyswitch, blown fuse, or bad wire (308-YL) in that circuit can be involved in triggering or masking this fault.
Will a weak or bad battery cause this code?
Yes, faulty batteries are listed as a possible cause. A battery that is overcharging, failing, or has internal damage can push voltage above the threshold that sets this code.