Diagnostic trouble code (DTC) information ECM-958F

Condition

Fig 1: Identifying PWM Signals From Accelerator Pedal Position Sensor To ETM

Courtesy of VOLVO CARS OF NORTH AMERICA.

The accelerator pedal position sensor has two different internal sensors, where one generates an analogue signal and the other a pulse-width modulated (PWM) signal. The sensor for the pulse-width modulated signal (PWM) is connected to both Engine control module (ECM) and Electronic throttle module (ETM). The sensor for the analogue signal is only connected to Engine control module (ECM). Engine control module (ECM) compares the analogue signal with the pulse-width modulated signal (PWM) coming from the accelerator pedal position sensor.

If Engine control module (ECM) registers that there is a difference of more than 5 % between the signals for longer time than 0.4 seconds, with the ignition on, then diagnostic trouble code ECM-958F, Faulty signal, is stored. At times when the analogue signal is in the process of changing, e.g., during acceleration, a greater deviation between both signals is allowed.

For upgraded software, released during year 2006 or later, certain adjustments have been made. For the test to be active, engine speed must be over 600 rpm and detection time must be increased from 0.4 to 0.7 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:

See Design
See Function

Substitute Value

Slow opening of throttle.

The throttle opens slower than during normal requested open because the system is regulated by only one of the pulse width modulated signals from the accelerator pedal position sensor. The driver may notice that the engine responds a bit slower compared to normal throttle application.

Closing of throttle during braking.

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

Possible Source

loose connections or contact resistance in the terminals on the analog signal cable
open-circuit in the power supply for the accelerator pedal (AP) position sensor
open-circuit in the ground lead for the accelerator pedal (AP) position sensor
fault in the PWM signal between the engine control module (ECM) and the electronic throttle module (ETM)
defective system relay
defective accelerator pedal (AP) position sensor.

This diagnostic trouble code is generated in combination with other trouble codes. Information on the possible root cause is described.

For turbo engines: Information about combined diagnostic trouble codes (DTCs)

For 5-cyl. normally aspirated engines. Information about combined diagnostic trouble codes (DTCs)

Fault symptom[s]

Poor accelerator pedal (AP) response.