Diagnosis Procedure

WARNING: This page is about a different car, the 2018 Nissan Titan XD. However, it is still accessible from the selected car via links, so may be relevant.

CHECK FOR CURRENT UREA HEATER RELAY CIRCUIT DTC
1. Turn ignition switch ON.
2. Connect CONSULT and check for existing "ENGINE" diagnostic trouble codes.
Is DTC P21C4-00 current?

YES

GO TO 2 .

NO

Refer to Intermittent Incident .
CHECK UREA HEATER RELAY CIRCUIT
1. Using CONSULT, erase existing "ENGINE" diagnostic trouble codes.
2. Turn ignition switch OFF.
3. Replace urea heater relay with a known good relay.
4. Turn ignition switch ON.
5. Using CONSULT, activate "DEF Tank Heater Test" and the "DEF Line Heater Test".
6. Using CONSULT, check "ENGINE" diagnostic trouble codes.
Is P21C4-00 DTC current?

YES

GO TO 3 .

NO

Relay was malfunctioning. Repair complete.
INSPECT DEF CONTROL MODULE AND CONNECTOR PINS
1. Turn ignition switch OFF.
2. Disconnect the DEF control module.
3. Inspect connector for the following:
  - Loose connector.
  - Corroded pins.
  - Bent or broken pins.
  - Pushed back or expanded pins.
  - Moisture in or on the connector.
  - Missing or damaged connector seals.
  - Dirt or debris on or in the connector pins.
  - Connector shell broken.
  - Wire insulation damage.
  - Damaged connector locking tab.
Is the inspection result normal?

YES

GO TO 4 .

NO

Repair or replace error-detected parts.

CHECK DEF HEATER SUPPLY CIRCUIT FOR SHORT TO OTHER CIRCUITS

Disconnect urea heater relay.
Check resistance between DEF tank heater supply circuit and all other circuits at the DEF control module harness connector.

DEF control module			Continuity
Connector	Terminal	Terminal	Continuity
C35	1	All others	No

Is the inspection result normal?

YES

GO TO 5 .

Repair short circuit in harness or connectors.

CHECK DEF HEATER SUPPLY CIRCUIT FOR SHORT TO VOLTAGE

Measure the voltage between the DEF heater supply circuit at the relay connector and ground.

Urea heater relay

Terminal (-)

Voltage

(Approx.)

Connector

Terminal (+)

E90

Ground

Was any voltage measured?

YES

Repair or replace the harness for a short to voltage source.
GO TO 6 .

Replace the DEF control module. Refer to Removal and Installation .
GO TO 6 .

ERASE CURRENT DTC
1. Connect all harness connectors.
2. Turn ignition switch ON.
3. Using CONSULT erase ENGINE diagnostic trouble codes.
4. Operate the engine within the "Conditions for setting the DTC".
5. Using CONSULT, check for "ENGINE" diagnostic trouble codes.
Is P21C4-00 DTC current?

YES

Return to Diagnosis Procedure. Refer to DTC Description .

NO

Repair complete.