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Hino P22A2 Fault Code: SCR outlet NOx sensor abnormal

08/11/2024

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TECHNICAL DESCRIPTION

NOx is detected by a NOx sensor status signal sent from NOx sensor 2 (SCR downstream).

DESCRIPTION OF MALFUNCTION

Failure of NOx sensor 2 (SCR downstream) is detected.

DTC SET CONDITION DTC

Detection Condition

NOx sensor is activated − |ΔFuel injection quantity (from ECM)| < 40 mg/cyl/sec.

Judgment Criteria:

The NOx sensor status signal sent from NOx sensor 2 is invalid for at least 90 second in a 180 second interval..

RESET CONDITION

After having restored to the normal conditions.

INDICATION, WARNING OR SYSTEM CONTROL REGULATION WHEN THE DTC IS SET

MIL: ON − DEF injection is stopped. − NOx reduction quantity monitoring is aborted

SYMPTOMS ON THE VEHICLE WHEN THE DTC IS SET

Symptoms on the Vehicle Due to Backup Control (Fail Safe Function):

Exhaust gas purification function is declined..

PRE-INSPECTION WORK

Check if the battery voltage is in the normal range.

AFTER-INSPECTION WORK

Clear all past DTCs. − Check if no DTC is stored after test drive

POSSIBLE CAUSES

Harness disconnection or short-circuit − NOx sensor 2 (SCR downstream) malfunction.

INSPECTION PROCEDURE

TROUBLESHOOTING STEPS

Step 1) Check the DTC detected (DCU) [Diagnostic Tool].

Set the starter switch to the “LOCK” position. 2. Connect the vehicle to the diagnostic tool.
Set the starter switch to the “ON” position.
Select [DCU] and check if any DTC other than P22A2 (for example, P22A0, P22A1, P22A7, U029E) has been detected.

Has a DTC other than P22A2 been detected?

Yes – Go to diagnosis procedure of a related DTC.

No – Go to Step 2.

Step 2) Inspect the NOx sensor 2 (SCR downstream) [Diagnostic Tool].

Set the starter switch to the “LOCK” position.
Disconnect the NOx sensor 1 (SCR upstream) and NOx sensor 2 (SCR downstream).
Install NOx sensors 1 and 2 in the vehicle, in their opposite location.
Set the starter switch to the “ON” position.
Erase the malfunction history using the diagnostic tool.
Perform a DPR forced regeneration.
Select [DCU] and check if P22A2 has been detected..

Has DTC P22A2 been detected?

Yes – Go to Step 3.

No – Replace the NOx sensor 2 (SCR downstream). Clear all past DTCs. Check if no DTC is stored after test drive.

Step 3) Inspect the engine coolant temperature sensor.

Check the installation of the engine coolant temperature sensor is properly installed.
Make sure there is no dirt or damage to the engine coolant temperature sensor.

Was any failure found?

Yes – Clean the engine coolant temperature sensor and install it properly. If damaged, replace the engine coolant temperature sensor. Clear all past DTCs. Check if no DTC is stored after test drive.

No – Go to Step 4.

Step 4) Check the engine coolant temperature sensor output signal [Diagnostic Tool].

Set the starter switch to the “ON” position.
Select [Engine].
Select [Engine coolant temperature] from [Data monitor Setting] on the menu.
When the engine coolant temperature (actual measured value) is 50°C {122°F}, check if the temperature output by the coolant temperature sensor is 50°C {122°F}.

Standard Values: Engine Coolant Temperature Sensor Output Value: 50°C {122°F} Do the measurements meet the standard value? Do the measurements meet the standard value?

Yes – Go to Step 5.

No – Replace the engine coolant temperature sensor. Clear all past DTCs. Check if no DTC is stored after test drive.

Step 5) Inspect the air flow sensor.

Check the installation of the air flow sensor.
Make sure there is no dirt or damage to the air flow sensor.

Was any failure found?

Yes – Go to Step 5.

No – Replace the engine coolant temperature sensor. Clear all past DTCs. Check if no DTC is stored after test drive.

Step 6) Inspect the boost pressure sensor.

Check the installation of the boost pressure sensor.
Make sure there is no dirt or damage to the boost pressure sensor.

Was any failure found?

Yes – If dirt, clogging or damage in the sensing unit was found, replace the boost pressure sensor. Clear all past DTCs. Check if no DTC is stored after test drive.

No – Go to Step 7.

Step 7) Check the boost pressure sensor output signal [Diagnostic Tool].

Start the engine.
Select [Engine] on the diagnostic tool.
Select [Actual boost pressure] from [Data monitor Setting] on the menu.
Race the engine from idle to No-Load Maximum and check if the boost pressure output signal varies.

Standard Values: Boost pressure sensor output value: There is no abnormal change in the sensor output signal. (The pressure sensor signal changes according to the engine speed). Do the measurements meet the standard value? Do the measurements meet the standard value?

Yes – Go to Step 8.

No – Replace the boost pressure sensor. Clear all past DTCs. Check if no DTC is stored after test drive.

Step 8) Inspect the intake manifold temperature sensor.

Check the installation of the intake manifold temperature sensor.
Make sure there is no dirt or damage to the intake manifold temperature sensor. Was any failure found?

Was any failure found?

Yes – Clean the intake manifold temperature sensor and install it properly. If damaged, replace the intake manifold temperature sensor. Clear all past DTCs. Check if no DTC is stored after test drive

No – Go to Step 9.

Step 9) Inspect the Intake manifold temperature sensor unit.

Set the starter switch to the “LOCK” position.
Disconnect the intake manifold temperature sensor connector.
Use the electrical tester to measure the resistance between the terminals of the intake manifold temperature sensor.

MEASUREMENT CONDITIONS	TESTER CONNECTIONS	STANDARD VALUES
Starter switch: LOCK	Intake manifold temperature sensor THG – E2	20°C {68°F}: 7.336 – 5.794 kΩ 50°C {122°F}: 2.435 – 1.994 kΩ

Do the measurements meet the standard value?