P10C9: reductant pressure sensor reference circuit fault

What this code means

P10C9 may indicate a reference voltage problem in the reductant pressure sensor circuit used by the diesel exhaust fluid system.

What the vehicle may do

The vehicle may display a service emissions or exhaust fluid warning.
The reductant system may be limited or disabled while the fault is active.
SCR dosing-related operation can be affected.

Possible fault areas

Possible reference voltage circuit fault
Possible low reference circuit fault
Possible signal circuit fault
Possible reductant pump and sensor assembly issue
Possible reductant control module issue

Diagnostic path

Opening: what P10C9 is telling you

On this Silverado 2500 diesel, P10C9 points you toward the reductant pressure sensor reference circuit. In plain terms, the control side may be seeing a reference voltage problem in the reductant pump and sensor circuit. The truck may display a service emissions or exhaust fluid warning, and the reductant injector, tank heaters, and pump can be disabled while the fault is active. Broadly, you’re checking the reference circuit, low reference, signal circuit, the reductant pump and sensor assembly, and the reductant control module. For this code, the setting condition is a 5 V Reference circuit short to ground, so keep the diagnosis electrical and prove the circuit before you condemn a component.

Start with the basic checks, then verify the fault

Before you get into pin testing, start with the basic system checks and follow a structured diagnostic approach. Then put the ignition on with the vehicle in Service Mode. If this code group is currently set, check what those codes mean first instead of jumping straight into this pinpoint test. If the code is not currently set, reproduce the operating conditions, or reproduce the captured conditions from the event data, and see if P10C9 resets. If it does reset, move into circuit testing. If it does not reset, the verification path is complete for now.

Low reference check

For the electrical testing, turn the ignition and all vehicle systems off. Give the vehicle time to power down; it may take up to 2 min before a ground or low reference continuity test is accurate. Disconnect the A38 Reductant Pump and Sensor Assembly connector. Test between Low Reference circuit terminal 3 and ground. You want less than 20 Ω. If that measurement is 20 Ω or greater, disconnect the K115 Reductant Control Module and check from Low Reference circuit terminal 3 at the component harness to terminal 21 at the control module harness. That check should be less than 2 Ω. If it is 2 Ω or greater, repair the open or high resistance in that circuit. If it is less than 2 Ω, the path points to replacing the K115 Reductant Control Module. If the original low reference test is less than 20 Ω, continue with the ignition on and the vehicle in Service Mode.

5 V reference circuit check

Next, test the 5 V Reference circuit at terminal 5 to ground. The expected range is 4.6 to 5.4 V. If it is less than 4.6 V, turn the ignition off, disconnect the K115 Reductant Control Module, and test terminal 5 at the component harness to ground for infinite resistance. If it is less than infinite resistance, repair the short to ground on that circuit. If it is infinite resistance, check terminal 5 at the component harness to terminal 19 at the control module harness. That should be less than 2 Ω. If it is 2 Ω or greater, repair the open or high resistance. If it is less than 2 Ω, replace the K115 Reductant Control Module. If terminal 5 to ground is greater than 5.4 V, turn the ignition off, disconnect the K115 module, turn the ignition back on with the vehicle in Service Mode, and test terminal 5 at the component harness to ground. You want less than 1 V. If it is 1 V or greater, repair the short to voltage. If it is less than 1 V, replace the K115 Reductant Control Module. If the original 5 V reference check is between 4.6 and 5.4 V, move on to the signal circuit.

Signal circuit checks

Now check the signal circuit. Test from Signal circuit terminal 4 to ground. The reading should be greater than 10 Ω. If it is 10 Ω or less, repair the short to ground on the signal circuit. If it passes, test from Signal circuit terminal 4 to Low Reference circuit terminal 3. That should be less than 1 V. If it is 1 V or greater, repair the short to voltage on the signal circuit. If it passes, test from Signal circuit terminal 4 to 5 V Reference circuit terminal 5. The expected range is 4.6 to 5.4 V. If that final signal-to-reference voltage is less than 4.6 V, pause on that signal-continuity branch and verify the intended specification before deciding between an open or high resistance repair and a module call; don’t guess on that branch. If the signal-to-reference voltage is between 4.6 and 5.4 V, replace the A38 Reductant Pump and Sensor Assembly.

After the component repair

After replacing the A38 Reductant Pump and Sensor Assembly, reproduce the operating conditions again, or reproduce the captured conditions from the event data. If P10C9 sets again after that repair, the next step is replacing the K115 Reductant Control Module. If the code does not set, that part of the test path is complete.

Final verification and message clearing

Keep final verification separate from the pinpoint testing. Once the repair is complete, verify the repair and confirm the code stays gone. If the driver information display shows Service Emission System or Service Exhaust Fluid System, run the Reductant System Tamper Warning Service Bay Test only under that message condition. That procedure clears the applicable driver information message. Bottom line: prove low reference, prove the 5 V reference, prove the signal circuit, then make the component call. For more diagnostic training, visit stepdiagnostics.com.