Diagnostic Trouble Code (DTC) Information ECM-902A

Condition

Fig 1: Identifying Signal Missing Between ETM And ECM

Courtesy of VOLVO CARS OF NORTH AMERICA.

The control modules communicate with each other in a network via standardized serial communication - CAN (controller area network). If the engine control module (ECM) detects that any of the electronic throttle module (ETM) signals on the CAN network disappear during operation for more than 0.32 seconds when engine speed is greater than 700 RPM, it stores the diagnostic trouble code.

For upgraded software, released during year 2006 or later, the above detection times are increased from 0.32 to 0.9 seconds.

See Identifying upgraded software ECM/ETM

For more information about the electronic throttle system and related components such as the electronic throttle module, accelerator pedal position sensor, brake light switch, clutch pedal position sensor, and brake pedal position sensor:Design Function

Substitute Value

Fuel cut-off that follows accelerator pedal position.

Engine speed is regulated via fuel cut-off by deactivating the injectors one at a time. Engine speed is determined by gas pedal position sensor position and engine speed is maximized to about 5000 RPM. This reconfiguration can cause the engine to idle very unevenly since the engine control module (ECM) regulates engine speed by cutting of the fuel to the cylinders individually. Do not confuse this reconfiguration (engine behavior) with an actual driveability problem that was present before reconfiguration.

Closing of throttle during braking.

The accelerator pedal position is ignored when the brake pedal is depressed.

Throttle follows accelerator pedal position.

The throttle and accelerator pedal are used as if they were mechanically connected. This reconfiguration is always followed by fuel cut-off.

Cruise control off.

Cruise control off during entire operating cycle in which fault was detected. If the fault is no longer present, the function is available the next time the car is started.

For upgraded software, released in 2006 or later, adjustments have been made to substitute values. In driving cycles when the fault is active, fuel shut-off that follows the accelerator pedal position will be activated.

See Identifying upgraded software ECM/ETM

Possible Source

Signal missing

delayed system relay start when the ignition is switched on
the power supply to the electronic throttle module (ETM) when the ignition is switched on (signal too high), or when running (signal missing)
loose connections or contact resistance in the terminals for the CAN
interference in the control area network (CAN) wiring
defective control area network (CAN) wiring
A control module in the CAN network is damaged.
This diagnostic trouble code is generated in combination with other trouble codes. Information on the possible root cause is described.
See Information about combined diagnostic trouble codes (DTCs)

Fault symptom[s]

the accelerator pedal (AP) is ignored when braking
the cruise control cannot be activated
uneven idle
jerks during engine braking.