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P1491

Read the instructions below then start the fault diagnostic procedure.

Symptom: CHECK ENGINE. Possible faulty reading on the fuel gauge in MIU.

P1491


Tank pressure sensor. Function faulty at the same time as the fuel level sensor diagnosis has reported a fault.


Fault symptoms


• CHECK ENGINE.

• Possible faulty reading on the fuel gauge in MIU.


On-Board Diagnostics

Type of diagnosis:


- Once per driving cycle. Interrupted when fault criteria fulfilled or OK reported. Restarts next driving cycle.


Enable criteria:


- General conditions for this trouble code: Atmospheric pressure must exceed 72 kPa and the engine coolant and intake air temperature must exceed -7°C.

- Accepted transition diagnosis of oxygen sensor 1. Purge active. Idling. Max. one change in status of brake light switch. Purge adaptation higher than -7%. Car stationary for 8 s.

The diagnosis will start once the above conditions have been fulfilled. If the diagnosis is interrupted then the speed must exceed 0 on one occasion before it is allowed to restart.


Fault criteria:


- Tank pressure pulsating at a frequency higher than 5.6 Hz with an amplitude exceeding 0.020 kPa.


Generation of diagnostic trouble codes:


- Fuel level, Plausibility diagnosis: Because fuel level is used as an enable criteria in certain diagnosis, then the control module must know that fuel level value is plausible. It works in such a way that Trionic receives the bus message ”Fuel level XX litre" from MIU. While driving Trionic observes the value and as the vehicle is driving it is consuming petrol, Trionic sees that the fuel level value will fall. In Trionic there is a number of filtrations of the value so as to avoid inaccuracies due to for example splashing fuel in the tank and hill starts. The fuel level diagnosis can be said to be a support diagnosis, it does not generate its own diagnostic trouble codes, but if for example the tank pressure sensor diagnosis has reported a performance problem in the tank pressure sensor then DTC P1451 is normally generated. If on the other hand the tank pressure sensor diagnosis has reported the same fault and the fuel level diagnosis at the same time has also reported a fault then DTC P1491 is generated instead.

Diagnostic trouble codes are generated if the fault criteria are fulfilled and the dependents are OK.


Dependents:


- P0444, P0445, P0501, P0502, P0506, P0507, P1444, P1445, P1576 and P1577.


System reaction to a fault:


- Integrity diagnosis of purge system blocked.


OK report:


- Diagnoses for P1451, P1452 and P1453 performed once and fault criteria not fulfilled. Fault criteria for P0452 or P0453 not fulfilled.


Fault handling: (For more information, see “Fault diagnosis, general".)


- Type III.


Diagnostic help

Fault diagnosis concerns an electrical fault in connecting leads or in the sensor.

Functions in the diagnostic tool related to the fault:


• Diagnostic status for the diagnosis.

• Tank pressure value, unit kPa. The value should be approx. 0 kPa with the filler cap removed. When the car is stationary, the value should be stable.


For more information, see “Fault diagnosis, general".

Checking the wiring

Jiggle the wiring harness at several points and in different directions to detect intermittent breaks and short circuits. Observe the multimeter, diagnostic tool or test lamp during the check.