Diagnostic Trouble Code (DTC) Information ECM-902B

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) has not received a CAN signal from the electronic throttle module (ETM) within 1.5 seconds of the engine being started and engine speed exceeding 700 RPM, diagnostic trouble code ECM-902B high signal is generated.

If the engine control module (ECM) has not received a system relay deactivation request from the electronic throttle module (ETM) within 10 seconds of the ignition being switched off, diagnostic trouble code ECM-902B low signal is generated.

For upgraded software, released during year 2006 or later, requires that battery voltage is above 9 V for the above tests to be performed.

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 too high

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.

Signal too low

Contact resistance, oxidation or poor contact in connections.
Low battery voltage at start-up.
Disruption or open-circuit on the Control area network (CAN).
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.