To Decide Operation Conditions When The Malfunction Was Detected
Malfunctions in a system may be intermittent. It is important to remember this when troubleshooting a possible malfunction cause. If the malfunction is not in the vehicle when it is in the workshop you can miss a malfunction cause since the values may be correct when troubleshooting takes place. A good indication of when the malfunction first occurred for the first time are the frozen values that can be read out for every diagnostic trouble code.
The frozen values are stored immediately after a malfunction has been detected. Most parameters in the frozen values are the same for all malfunctions and indicate a general condition when a malfunction has been detected, e. g., engine RPM, load, coolant temperature, vehicle speed and battery voltage. Some of them have been selected to give a better understanding of the specific malfunction.
Diagnostic trouble code ECM-903F Electronic throttle unit, internal malfunction cam be used as an example of how frozen values can be used.
The first possible source indicated in VIDA (Volvo scan tool) is the voltage feed to the electronic throttle unit and then continues by suggesting that you check the battery and charging system. However, the battery's condition when the vehicle is in the workshop does not necessarily show the battery voltage when the malfunction was detected.
Instead, the best information is found in the frozen values, that is, voltage that the Engine control module (ECM) detects when Electronic throttle module (ETM) indicated the malfunction.
However, you should remember that this is not an indication of voltage feed to Electronic throttle module (ETM), it is voltage feed to Engine control module (ECM). If Engine control module (ECM) according to frozen values has had good voltage the battery was okay. Therefore, voltage feed to Electronic throttle module (ETM) should be checked separately.
Frozen values for ECM 903F:
- Condition, heated oxygen sensor control bank 1 = LR: Closed circuit with two sensors
- Condition, heated oxygen sensor control bank 2 = LR: Closed circuit with two sensors
- Calculated load = 4.71%
- Engine temperature = 87 °C
- Fuel adaption, quick adjustment, bank 1 = 15.63%
- Fuel adaption, slow adjustment, bank 1 = -0.78%
- Fuel adaption, quick adjustment, bank 2 = 23.44%
- Fuel adaption, slow adjustment, bank 2 = -0.78%
- Engine speed = 760 RPM
- Vehicle speed = 0 km/h
- Boost pressure = 30%
- Battery voltage = 12.50 V
- Throttle angle, desired value = 14.84%
- Air mass = 23.8 kg/h
- Outside temperature = 33 °C
In this case we assume that the vehicle had low battery voltage in the workshop. However, as can be seen in the frozen values, battery voltage was okay when the malfunction occurred, so this was probably not the cause.
This is an example of how frozen values can be used to increase efficiency of troubleshooting and av avoid using too much time for incorrect troubleshooting. This prevents troubleshooting and fixing a malfunction that was not the real cause of the problem that was to be solved.
The odometer reading (km) is sometimes included in frozen values in Engine control module (ECM). This enables a quick comparison with the odometer so that you can assess if the malfunction occurred as part of the troubleshooting and can be ignored. For example, CAN-network-related diagnostic trouble codes are saved when the battery voltage drops during work on the vehicle since passenger compartment lighting and other loads drain the battery.
The frozen values indicate odometer reading in km. If you multiply this value by factor 0.62 you obtain driving distance in miles. Current driving distance in both miles and km can be read out with VIDA (Volvo scan tool).
Keep the following in mind when using frozen values for troubleshooting.
The frozen values to be used with care are those stored for the CAN-net and are related to diagnostic trouble codes for Electronic throttle module (ETM).
If Electronic throttle module (ETM) detects that communication to Engine control module (ECM) is interrupted, then malfunction flags will be generated in Electronic throttle module (ETM). These malfunction flags will be sent to Engine control module (ECM) first when communication on the CAN-net works again.
This means that Engine control module (ECM) will store the diagnostic trouble codes first when Electronic throttle module (ETM) delivers them, which in turn means that it is at this point in time that the frozen values are saved. For Electronic throttle module (ETM) this means that the frozen values will be from a point in time after the malfunction first occurred.