CAT Engine 1682 Fault Code: System Voltage intermittent/erratic
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System Voltage intermittent/erratic · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
CAT code 1682 (SPN 168 FMI 2) sets when the ECM sees battery voltage drop below 9 VDC intermittently, or below 9 VDC three times in 7 seconds, or in some ECM versions below 6 VDC and back above 9 VDC three times in 7 seconds, while the engine is running. It points to an unstable power supply to the ECM, not a normal low-battery warning, and can cause misfires, rpm changes, or complete shutdown.
High severity. This code can cause engine misfire, unexpected rpm changes, or a complete engine shutdown while running. It is not an emergency stop-now code by itself, but intermittent power to the ECM should be diagnosed before the next operating shift because repeat failures can leave the machine stranded or shut down without warning.
What does CAT Engine error code 1682 mean?
CAT fault code 1682 (SPN 168, FMI 2) means the engine's Electronic Control Module is seeing erratic, intermittent, or incorrect voltage on its battery power input while the engine is running. The ECM runs off constant battery power fed through a circuit breaker, plus a switched signal from the keyswitch that tells it to power up. If either supply flickers or sags, the ECM logs this code.
Depending on the ECM version, the trigger is voltage dropping below 9 VDC intermittently, or below 9 VDC three separate times within 7 seconds. Some ECM versions instead look for voltage falling below 6 VDC and then recovering above 9 VDC, three times within 7 seconds.
This is different from a dead battery. The engine is already running when this fault sets, so the problem is usually a poor connection, damaged wiring, a failing keyswitch, or a marginal battery or charging system that cannot hold steady voltage under load.
What triggers a CAT Engine 1682 code?
The ECM logs 1682 when, with the engine running (not cranking) and keyswitch ON, battery voltage drops below 9 VDC intermittently, or drops below 9 VDC three times within 7 seconds. On some ECM versions the threshold is voltage falling below 6 VDC and then returning above 9 VDC, three times within 7 seconds. Related low-voltage codes (168-00, 168-01, 168-02) may also be active or logged alongside this fault.
Common causes of 1682
- Connector, pins, or sockets not fully coupled or inserted at the ECM or in the battery/keyswitch circuit
- Harness or wiring damaged by corrosion, abrasion, or pinch points
- Negative battery wires damaged or in need of repair
- Weak, faulty, or undercharged batteries that need recharging or replacement
- Damaged or high-resistance wiring between the battery and the 15 amp circuit breaker, or between the breaker and the ECM connector P1
- Faulty or worn keyswitch, or a wiring problem between the keyswitch and the ECM (including wire 308-YL on some models)
- Main power relay or load reduction relay circuit fault
- Problem in the charging system or starting system feeding the batteries
- Faulty ECM (checked only after wiring, batteries, and keyswitch are confirmed good)
How to troubleshoot CAT Engine 1682: first checks
- Rule out the starting system and charging system first. Confirm batteries hold a steady charge and the alternator is charging correctly before testing ECM wiring.
- Inspect all ECM harness connectors for corrosion, bent pins, or connectors that are not fully seated. Check terminals P1-48, P1-52, P1-53, P1-55 (+Battery) and P1-61, P1-63, P1-65, P1-67 (-Battery) where accessible, and confirm the keyswitch signal is present at P1-70.
- Check the wiring and connections between the batteries and the 15 amp circuit breaker, and between the breaker and the ECM connector, for abrasion, pinch points, or loose connections.
- Test the keyswitch: confirm voltage is present on terminal B (battery side). If not, repair the circuit between +Battery and the keyswitch and check the circuit protection. If voltage is present on terminal B but not on terminal R, replace the keyswitch.
- Check continuity of the wire between the keyswitch and the ECM for a short or an open circuit.
- If an engine shutdown was accompanied by a loss of other electrical accessories, suspect the keyswitch or the load reduction relay circuit rather than ECM wiring.
- If all wiring, connectors, batteries, and the keyswitch check good, consider the ECM itself as a last-resort cause.
How the code clears
No separate clearing step is listed beyond correcting the root cause. Repair or replace the faulty wiring, connector, battery, or keyswitch as needed, then clear the logged diagnostic code. Note that rapidly cycling the keyswitch can itself generate logged codes, so clear old codes after repair to avoid confusion during future diagnosis.
Affected models and serial ranges
1682 appears in our records across 10 CAT Engine models. Match your machine by model and serial number.
| Model | Serial ranges |
|---|---|
| C10 | Serial range not listed in source records |
| C11 | Serial range not listed in source records |
| C12 | Serial range not listed in source records |
| C13 | Serial range not listed in source records |
| C15 | Serial range not listed in source records |
| C16 | Serial range not listed in source records |
| C175 | Serial range not listed in source records |
| C18 | 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 code 1682 mean?
It means the engine ECM detected erratic, intermittent, or incorrect battery voltage on its power input while the engine was running. This is SPN 168, FMI 2, and it points to an unstable electrical supply to the ECM rather than a simple dead battery.
Can I keep driving or operating with code 1682 active?
It is not recommended. The fault can cause the engine to misfire, change rpm unexpectedly, or shut down completely while running. Diagnose the electrical connections, batteries, and keyswitch before continuing normal operation.
What voltage triggers code 1682?
Depending on the ECM version, it triggers when voltage drops below 9 VDC intermittently or three times within 7 seconds, or on some ECM versions when voltage falls below 6 VDC and recovers above 9 VDC three times within 7 seconds, all while the engine is running.
Is code 1682 a battery problem or a wiring problem?
It can be either. Listed causes include weak or faulty batteries, corroded or damaged wiring and connectors, a failing keyswitch, damaged negative battery wires, or a bad main power relay. A faulty ECM is possible but should be the last thing checked.
Why did my engine shut down along with loss of other electrical accessories?
That pattern points to a problem in the keyswitch or the load reduction relay circuit, not the ECM wiring itself. Check the keyswitch and that relay circuit first.
Does cycling the keyswitch cause this code?
Rapidly cycling the keyswitch can generate logged codes on its own. If this happened, clear the logged codes afterward so they do not cause confusion or an incorrect diagnosis later.
Which CAT engines can set code 1682?
This code applies to the C10, C11, C12, C13, C15, C16, C175, C18, C27, and C32 engine models.