CAT 13 Fault Code: Fuel Temperature voltage high
Fuel Temperature voltage high · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
CAT fault code 13, SPN 174 FMI 3, means the ECM has detected the fuel temperature sensor signal voltage is out of the expected range, either too high or too low, on C11, C13, C15, and C18 engines. This points to a wiring, connector, or sensor problem in the fuel temperature circuit rather than an actual fuel temperature event.
Medium severity. This code does not by itself indicate an immediate engine-damage risk, but an unreliable fuel temperature reading can affect fuel system calculations and should be diagnosed within the shift rather than ignored.
What does CAT error code 13 mean?
Fault code 13 (SPN 174 FMI 3) is set when the Engine Control Module (ECM) sees the fuel temperature sensor signal voltage sitting outside its valid operating range. The ECM uses this sensor to know how hot or cold the fuel is, which factors into fuel delivery calculations on C11, C13, C15, and C18 engines.
There are two distinct voltage conditions that trigger this code. One is a high-voltage condition where the signal reads greater than 4.95 VDC for more than eight seconds, alongside engine coolant temperature above -10 degrees C (15 degrees F) and the ECM having been powered for at least two seconds. The other is a low-voltage condition where the signal reads less than 0.2 VDC for more than eight seconds.
In both cases, the ECM is not reading a real fuel temperature, it is reading a circuit fault. That means the fix is almost always electrical: a bad connection, damaged harness, or failed sensor, rather than anything wrong with the fuel itself.
What triggers a CAT 13 code?
The ECM sets this code under two separate conditions. High-voltage condition: fuel temperature sensor signal voltage greater than 4.95 VDC for more than eight seconds, with engine coolant temperature above -10 degrees C (15 degrees F) and the ECM powered for at least two seconds. Low-voltage condition: fuel temperature sensor signal voltage less than 0.2 VDC for more than eight seconds.
Common causes of 13
- ECM connection problems (corroded, loose, or damaged connector pins)
- ECM harness damage or wiring faults between the ECM and the fuel temperature sensor
- Fuel/engine temperature sensor failure
- Fuel/engine temperature sensor harness damage or poor connection
- Active 5 Volt Supply voltage codes (232-3 or 232-4) causing the low-voltage condition, if present these should be diagnosed first
- ECM internal failure (for the low-voltage condition, listed as a possible but less likely cause)
How to troubleshoot CAT 13: first checks
- Check the ECM connector and the fuel temperature sensor connector for corrosion, moisture, loose pins, or physical damage
- Inspect the wiring harness between the ECM and the fuel temperature sensor for chafing, pinches, or breaks
- If code 232-3 or 232-4 (5 Volt Supply voltage codes) is also active, diagnose and resolve those first before continuing on this code
- Test the fuel temperature sensor signal circuit for the voltage conditions described (high above 4.95 VDC or low below 0.2 VDC) to confirm which condition is present
- If wiring and connectors check out, test or replace the fuel temperature sensor itself
- If the sensor and harness both test good, consider ECM failure as a last-resort cause for the low-voltage condition
How the code clears
No separate clearing step is listed for this code. Once the underlying wiring, connector, or sensor issue is repaired and the signal voltage returns to a valid range for the required time, the ECM should stop setting the fault on its own. Confirm with a diagnostic tool that the code is no longer active after the repair.
Affected models and serial ranges
13 appears in our records across 4 CAT 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 |
| C18 | Serial range not listed in source records |
Frequently asked questions
What does CAT fault code 13 mean?
It means the ECM has detected the fuel temperature sensor signal voltage is outside the normal range, either too high (above 4.95 VDC for more than eight seconds) or too low (below 0.2 VDC for more than eight seconds). It is a circuit fault, not an actual overheating or freezing fuel condition.
Which CAT engines can show fault code 13?
This code applies to the C11, C13, C15, and C18 engine models.
Is fault code 13 dangerous to keep driving with?
It is not typically an immediate safety emergency, but it means the ECM cannot trust its fuel temperature input, which can affect fuel delivery calculations. It should be diagnosed and repaired within the same shift rather than run indefinitely.
Should I check other codes before working on fault code 13?
Yes. If code 232-3 or 232-4 (5 Volt Supply voltage codes) is active, troubleshoot those first, since they can cause the low-voltage version of fault code 13.
What usually causes CAT fault code 13?
The most common causes are connector or harness problems at the ECM or fuel temperature sensor, or a failed fuel temperature sensor. ECM failure is possible but less common and is listed only for the low-voltage condition.
How do I know if I have the high-voltage or low-voltage version of this fault?
You need to check the actual signal voltage at the sensor circuit. Above 4.95 VDC for more than eight seconds is the high-voltage condition; below 0.2 VDC for more than eight seconds is the low-voltage condition. Each has a slightly different list of probable causes.
Is there a reset procedure for fault code 13?
No reset procedure is listed for this code. Repairing the underlying wiring, connector, or sensor issue should allow the ECM to clear the fault once the voltage reads within a valid range.