SPN 168 FMI 0 is the Detroit DD Series diagnostic trouble code for battery voltage high, and this page documents its official engine charging and battery power circuit troubleshooting sheet. This concise single-page sheet targets an over-voltage condition on the battery and charging system, where the Common Powertrain Controller reads a supply voltage above the normal operating range. It is a fast confirmation test rather than a long tree, so it focuses the technician on the alternator and its voltage regulator as the most likely source.
SPN 168 FMI 0 document details
| Brand | Detroit |
| Model coverage | DD Series — DD13, DD15, DD16 |
| System / group | DD Series (EPA 2007-Current) / DTCs |
| SPN | 168 |
| FMI | 0 |
| Fault | Battery Voltage High |
| Emissions / revision | All years — Copyright 2017 |
| Pages | 1 |
| File size | 0.2 MB |
| Format | |
| Language | English |
Document table of contents
- Fault description: battery voltage high
- Measure battery voltage at maximum rpm
- Over-16-volt alternator check
- Alternator repair or replacement decision
Troubleshooting steps summarised
The technician measures battery voltage with the engine running at maximum rpm. If the reading is greater than 16 volts, alternator operation is checked and the alternator is repaired or replaced as required. Because a sustained over-voltage condition can damage lamps, control modules and the battery bank, the sheet keeps the diagnosis deliberately short and points straight at the charging output rather than the sensing circuit.
Applicable truck models covered
The document applies across all model years of the Detroit DD Series (DD13, DD15 and DD16) monitored by the Common Powertrain Controller charging circuit, whether the engine is installed in a linehaul tractor, a vocational chassis or a coach. For engine specifications and warranty coverage, refer to the official Demand Detroit service resources. These troubleshooting steps are cross-checked with the Detroit Diesel Diagnostic Link (DDDL) and the official Demand Detroit service resources.
Who needs this SPN 168 FMI 0 guide
Technicians confirming an over-charging alternator, a failed voltage regulator, or a high battery-voltage warning on the dash use this short sheet to verify the fault quickly at maximum engine speed before condemning the alternator or the battery pack.
The full PDF is available in the DiagTechPro manuals library; a free account is required to download the complete step-by-step document.
Related manuals library
