Code Details
| Display code | Navistar Aware SPN 158 FMI 4 |
|---|---|
| SPN | 158 |
| FMI | 4 |
| OEM code | Navistar / International Aware SPN 158 FMI 4 |
| Manufacturer | Navistar / International |
| System | Aware Vehicle Intelligence / Telematics |
| Component | Power supply — voltage below normal |
| 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 at Black connector Pin 1 is not receiving sufficient voltage — below 9 volts, which is the lower threshold for normal operation. This can mean the module is losing its power source, there is a significant voltage drop in the supply wiring, or the vehicle's electrical system is below normal charging voltage.
Navistar S08312 maps Navistar Aware SPN 158 FMI 4 to Battery Potential — voltage below normal or shorted low at Black connector Pin 1. The fault activates when voltage falls below 9 volts for more than 1 minute while ignition is on.
Common Symptoms
- Aware Vehicle Intelligence alert active — may correlate with engine start, heavy electrical load, or battery condition
- Module may reset or lose communication during the low-voltage event
- Fleet portal may show a short offline period that matches the low-voltage timestamp
- Fault can be most common after cold starts, liftgate operation, inverter use, or long key-on engine-off periods
Possible Causes
Possible causes may include the items below. The list is not a parts diagnosis.
- Battery in poor condition causing voltage to drop below 9 V during load conditions
- High-resistance connection in the Aware module's supply circuit causing excessive voltage drop under load
- Fuse or fuse holder with high resistance limiting supply voltage
- Alternator not charging — battery discharging during operation
First Checks
- Measure the voltage at Black connector Pin 1 under load conditions — compare to battery voltage to identify voltage drop in the circuit.
- Check the vehicle's charging system voltage and battery condition.
- Inspect fuse holders and supply wiring connections for resistance.
- Perform a voltage drop test from battery positive to Black connector Pin 1 and from the module ground back to battery negative while the module is powered.
- If the vehicle battery voltage is also below 9 V during the fault, the electrical system — not the Aware module wiring — is the source.
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
Is 9 volts the minimum the Aware module needs to operate?
9 volts is the fault threshold, not necessarily the minimum operating voltage. The module may continue operating below 9 V for a time, but it flags the fault to indicate it is operating outside its normal supply range. Sustained operation below 9 V can affect reliability and data quality.
Can this fault appear only at engine start?
Yes. Engine cranking draws high current, which can pull battery voltage below 9 V briefly. If the fault only appears during cranking and clears immediately after the engine starts, a battery with reduced cold cranking capacity is a likely cause.
Does Navistar Aware SPN 158 FMI 4 affect HOS or fleet data?
If the Aware module loses power or operates below specification, telematics data collection may be interrupted for the duration of the low-voltage event. Position, J1939 data, and any active monitoring may have gaps corresponding to the power event.