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P1491

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

P1491


EVAP Tank Pressure Sensor. Performance Problem at the same time as the fuel level sensor diagnosis has reported a fault.


Fault symptoms


• CHECK ENGINE.

• Possible faulty readings on the fuel gauge in the 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 condition for this diagnostic trouble code: Atmospheric pressure must exceed 72 kPa as well as 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.


Generating diagnostic trouble codes


- Fuel Level, plausibility diagnosis: Because the fuel level is used as enable criteria in certain diagnoses, the control module must know that the fuel level value is plausible. The way it works is that the Trionic receives a bus message ”Fuel level XX litres" from the MIU. During driving the Trionic observes the value and as the car is driven, fuel is consumed. The Trionic makes sure the fuel level value drops. In the Trionic a number of important filtrations are carried out to avoid faults caused by, for instance, splashing fuel in the tank, starting uphill. The fuel level diagnosis can be called a support diagnosis as it does not generate a DTC, but if for instance the EVAP tank pressure sensor diagnosis has reported performance problems in the EVAP 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 has simultaneously reported a fault then DTC P1491 is generated instead.

Diagnostic Trouble Codes are generated if the fault criteria are fulfilled and the dependants 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 handling III, other emission-related components and functions )

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 Menu "Read Values" .

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.