Code Details
| Display code | Navistar Aware SPN 168 FMI 2 |
|---|---|
| SPN | 168 |
| FMI | 2 |
| OEM code | Navistar / International Aware SPN 168 FMI 2 |
| Manufacturer | Navistar / International |
| System | Aware Vehicle Intelligence / Telematics |
| Component | Power supply — battery voltage erratic |
| Source address | Unknown or not applicable |
| Severity | medium |
| Review status | ai source checked |
| Source confidence | high |
| Last reviewed | 2026-03-26 |
Plain-English Meaning
The Aware module monitors the actual voltage it receives at its power input and compares it to the battery voltage broadcast over J1939 by the engine ECM. A gap of more than 2 volts that persists for a minute suggests either a wiring resistance problem (voltage drop in the Aware module's power supply circuit) or an issue with the J1939 reference value.
Navistar S08312 maps Navistar Aware SPN 168 FMI 2 to Battery Potential — data erratic, intermittent or incorrect at Black connector Pin 1. The Aware module cross-references its local voltage measurement against the engine ECM's J1939 broadcast of battery voltage. A deviation exceeding 2 volts for 60 seconds triggers the fault.
Common Symptoms
- Aware Vehicle Intelligence alert active while vehicle is operating
- Battery voltage in Aware diagnostic data differs noticeably from what the scan tool shows on the engine ECM
- Fault may appear only when the module wakes up under accessory load or when the engine transitions from crank to idle
- Fleet portal reports may show short communication gaps even though the truck continues running normally
Possible Causes
Possible causes may include the items below. The list is not a parts diagnosis.
- High resistance in the Aware module's power supply wiring — corroded fuse holder, loose ring terminal, or undersized wire causing significant voltage drop
- Aware module drawing more current than expected due to an accessory load on the same circuit
- J1939 battery voltage broadcast from the engine ECM is inaccurate due to a separate sensor or calibration issue on the engine side
First Checks
- Measure the voltage at Black connector Pin 1 and compare it directly to the battery terminal voltage with the engine running.
- Check for voltage drop in the Aware module's power supply circuit: measure voltage at the source, at any fuse holder, and at the module.
- If the Aware voltage and the battery terminal voltage match closely, the fault may originate from the engine ECM's broadcasted voltage value — check the engine ECM's voltage sensor.
- Inspect the power supply wiring for corroded or high-resistance connections.
- Repeat the voltage comparison with headlights, HVAC blower, liftgate, inverter, or other large accessories turned on; marginal wiring often passes at idle load and fails under accessory load.
Can I Keep Driving?
Severity depends on active status, warning lamps, affected system, and related codes. Stop safely for red stop lamps, brake warnings, oil pressure warnings, high coolant temperature warnings, severe derate, or any abnormal vehicle-control concern.
Related Lookup Pages
Sources
- Navistar Aware Vehicle Intelligence Diagnostic Trouble Codes S08312 Navistar / International Truck Body Builder · oem · accessed 2026-05-05 · confidence high
Source: Navistar / International Truck Body Builder, Navistar Aware Vehicle Intelligence Diagnostic Trouble Codes S08312. This page paraphrases factual fields only and is not a substitute for the original document.
Open source - Navistar Engine Diagnostic Trouble Code Body Builder References Navistar / International Truck Body Builder · oem · accessed 2026-05-05 · confidence medium
Source: Navistar / International Truck Body Builder, Navistar Engine Diagnostic Trouble Code Body Builder References. This page paraphrases factual fields only and is not a substitute for the original document.
Open source
FAQ
How does the Aware module know what the engine ECM is reporting for battery voltage?
The Aware module reads the battery potential SPN from the J1939 bus, which the engine ECM broadcasts. If the Aware module has a good J1939 connection, it can compare its directly measured voltage with the ECM's reported value. A discrepancy indicates either a measurement path difference or a fault in one of the sensing paths.
Can a weak battery cause Navistar Aware SPN 168 FMI 2?
A weak battery can cause voltage to drop unevenly — the voltage at the battery terminal may differ from the voltage at the Aware module's supply if there is resistance in the circuit. Under high current demand, a marginal battery can also create a larger voltage gradient across the supply wiring.
Is Navistar Aware SPN 168 FMI 2 a safety concern for the vehicle?
This fault is specific to the Aware telematics module's power quality and does not affect engine, brake, or powertrain systems. However, a significant voltage discrepancy in the Aware supply circuit may indicate a wiring issue worth investigating before it affects other electrical systems.