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OBD-II Diagnostic Trouble Code

P0168 — Fuel Temperature Sensor Range/Performance

P0168 means the fuel temperature sensor reading does not make sense compared with other temperature inputs or with how fuel temperature should change. For example, it may read far from coolant and intake air temperature after a long cold soak, or never change during operation. On diesels the sensor is often in the fuel filter head, the pump or the return circuit, and the ECM uses it to correct fuel density and injection quantity. Newer SAE revisions and many manufacturers define P0168 as fuel temperature too high instead, so check the OEM definition.

Severity 2/5 Truck-relevant
Service soon
Severity
Service soon Fuel Temperature Sensor Range/Performance
Code
P0168
Category
Powertrain
Subsystem
Fuel
Truck-relevant
Yes
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What this means for truckers

Service this week on a Cummins X15, Detroit DD15, PACCAR MX-13. Not an immediate stop, but ignoring it usually leads to a more expensive fix downstream.

Before you replace parts — try this first

P0168 on the Fuel system is most often fuel temperature sensor out of calibration or failing — not a dead part. On commercial diesels especially, work these in order before spending money on parts:

  1. Confirm the symptoms. Match what your truck is doing to the Symptoms section below. If the code is set but the symptoms are not there, clear the code and re-test after a drive cycle — it may not return.
  2. Clean and dry the sensor connector. Water, road salt, or oil seeping into a connector is the #1 fake sensor failure. Disconnect, look for green corrosion or moisture, spray with electrical contact cleaner, dry, reseat. Many faults clear here for $0.
  3. Inspect the wiring harness. Trace the wire from the sensor toward the ECM — look for chafing against the engine block, melted insulation near the turbo or exhaust, or pinch points where a clamp has rubbed through.
  4. Test the sensor before swapping it. Most Common Causes (below) list the expected voltage or resistance range — a $20 multimeter saves a $300 sensor swap that does not fix the problem.
  5. Only then, replace the part. Use the OEM or a tier-1 aftermarket. Cheap sensors throw the same code in two weeks.
Symptoms

Check-engine light is on. On diesels you may notice slightly reduced power or a mild derate, because the ECM may use a default fuel temperature value. Fuel economy may change a little. If the fuel really is overheating, as with heavy return flow or low tank level in hot weather, power loss can be more noticeable.

Common causes
  • CommonFuel temperature sensor out of calibration or failing ($80–$300)
  • CommonCorroded connector or high resistance in the sensor wiring ($80–$300)
  • OccasionalFuel actually running hot, from a low tank level, a restricted fuel cooler or excessive return flow from worn injectors or a worn pump ($150–$1500)
  • RareECM input or software issue ($150–$2000)
How to fix
After an overnight cold soak, compare fuel temperature with coolant and intake air temperature on a scan tool. They should be close to each other.
When to use: To check sensor plausibility
Measure sensor resistance at a known temperature against the spec chart, and inspect the connector for corrosion or fuel contamination.
When to use: When the reading is clearly off
Check fuel cooler condition and return flow when the fuel really is reading hot. Replace the sensor if it fails the resistance test.
When to use: Depending on whether the fuel is truly hot or the sensor is wrong
Affects most

No specific vehicle pattern found in our complaint database. This code can appear on any vehicle that supports OBD-II diagnostics.

Related

Frequently Asked Questions

Can I drive with code P0168?
P0168 is severity 2 — service this week. Not an immediate stop, but ignoring it usually compounds the problem. Most common cause for this code is a worn sensor or minor performance fault that won't strand you today but will get more expensive the longer you wait.
How much does it cost to fix P0168 on a commercial truck?
Total repair cost ranges $80–$2000 depending on the root cause. The cheapest fix is usually the first one listed below — Fuel temperature sensor out of calibration or failing — which is also the most common. On commercial trucks the cost is usually higher than passenger vehicles due to part availability and shop labor rates ($120–185/hour at most truck shops, vs $90–130 at general auto shops). DIY-capable fixes (sensors, hoses, filters) are at the low end; major component replacements (turbo actuator, high-pressure fuel pump, transmission solenoid pack) are at the high end. Always diagnose with a scan tool BEFORE replacing parts — guessing wrong on a $1,500 turbo actuator when the actual issue was a $30 boost hose is a common expensive mistake.
Will P0168 fail a DOT inspection?
P0168 itself doesn't automatically fail an inspection, but if the truck is in reduced-power mode (limp mode) at the time of inspection, it WILL be flagged. Most inspectors will note the check engine light but pass the truck if it's running and performance is normal. Fix it before a Level 1 inspection regardless.
What's the difference between P0168 and related codes?
P0168 is closely related to: P0100 (Mass or Volume Air Flow Circuit), P0101 (Mass or Volume Air Flow Circuit Range/Performance), P0102 (Mass or Volume Air Flow Circuit Low Input), P0103 (Mass or Volume Air Flow Circuit High Input). These codes share the same subsystem (fuel) and often appear together. If you see this code, scan for the full code list — fixing the root cause usually clears multiple companion codes at once. If only P0168 is set without the companions, the issue is more isolated.
How do I prevent P0168 from coming back after a repair?
For P0168 (Fuel Temperature Sensor Range/Performance), prevention centers on the fuel system. Replace fuel filters at the OEM interval — don't stretch them. Use only diesel from high-volume fuel stops (avoid bottom-of-tank fuel at low-traffic stations). Add a water separator if you don't have one. After repair, prime the fuel system per the engine manual.

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