P24F3: Reductant Tank Temperature/Fuel Temperature Correlation

What it means

After a long key-off soak the AdBlue/DEF tank temperature and the fuel tank temperature should read close to each other (both at ambient). The ECM detects an implausible spread, which usually means one of the two sensors drifts, is wired wrong, or has a heat source nearby that the plausibility model does not account for.

At a glance

• Usually lights the check-engine light
• Affects emissions; the car can fail an emissions test

How it works

The reductant tank temperature sensor measures the temperature of the AdBlue/DEF fluid, while the fuel temperature sensor measures fuel temperature. After a long key-off soak, the control module expects both readings to be near ambient and close to each other. P24F3 sets when their difference is implausible, including when one sensor drifts or a recently used reductant heater leaves the tank warm.

Common causes

Most likely first.

1. One temperature sensor drifting outside tolerance
2. Recently active reductant tank heater warming the tank above ambient

Symptoms

• Check engine light may illuminate

How to diagnose it

1. Check freeze-frame data and recent operating history to see whether the reductant tank heater was active before the fault.
2. After a long cold soak, compare reductant tank and fuel tank temperature readings on a scan tool before starting the vehicle.
3. Inspect both temperature sensor connectors and harnesses for corrosion, damage, crossed wiring, or heat exposure.
4. Compare each reading with ambient temperature to determine whether the reductant tank or fuel temperature value is the outlier.
5. Test the reductant tank temperature sensor and fuel temperature sensor circuits and response against the manufacturer's specification.
6. If sensor readings and wiring pass, repeat the comparison after a suitable soak without recent heater operation and check for other conditions affecting tank temperature.

Common fixes

• Repair damaged or corroded wiring at the reductant tank or fuel temperature sensor.
• Allow the tank to cool and repeat the check if recent reductant heater operation explains the temperature spread.
• Replace the reductant tank temperature sensor if its reading or response fails the manufacturer's specification.
• Replace the fuel temperature sensor if its reading or response fails specification.

Can I keep driving?

The code by itself generally does not indicate an immediate driving hazard, but it can interfere with emissions monitoring. Arrange diagnosis, especially if an aftertreatment warning or reductant countdown appears.