Practical Use Of Diagnostics
Practical use of diagnostics
General
There are several ways to decide if the malfunction is active right now or not as well as when the malfunction occurred:
- Read off the diagnostic trouble code's counter, status identifier and frozen values. By interpreting these you can find out when the malfunction was stored, how often the malfunction has occurred (intermittence) and what the driving conditions were when the malfunction was stored.
- Read off a parameter for component/system and decide if the value is correct or not. By, e.g., manually affecting the sensor or the switch, you can decide immediately if the parameter (signal) with its circuit is correct.
- Trigger a component (activate) and decide if the component/function is affected or not. By triggering, e.g., the relay and listening for its clicking sound or the function which is to be affected, it is possible to decide immediately if the component is correct.
- Decide if the vehicle shows any symptom (malfunction). If the vehicle no longer shows the symptom, one may suspect that the malfunction no longer is active.
The following accounts in detail for some of the above.
To decide the intensity of a malfunction
Note! Examples 1-5 (below) are based on counters for diagnostic concept Generic Global Diagnostic (GGD).
When a malfunction is intermittent or has unknown status, the diagnostic trouble code's counter is very useful to decide:
- How many driving cycles that have passed since the malfunction was detected the first time as well as since the malfunction was detected.
- During how many driving cycles that the control module has detected the malfunction during a certain period, as well as how many driving cycles that the control module has not detected the malfunction. That the control module has not detected the malfunction may be due to the control module not having started the test for the malfunction, conditions to detect the malfunction are not fulfilled, or that the malfunction no longer exists.
The purpose of interpreting the counters is that it is possible to understand the malfunction's intensity, that is, show "how much" intermittent the malfunction is, as well as help in assessing if the chances to repeat the malfunction and customer symptom, and then succeed with troubleshooting.
If you read out the diagnostic trouble code information and it shows that the diagnostic trouble code test runs at least once every driving cycle (e.g., when driving), the counters' value may be very important when assessing the diagnostic trouble code's status and actions. However, if start of diagnostic trouble code test and its conditions are difficult to achieve, the counters' values should be considered to be of less importance.
Counters 1 and 3 show driving cycles. Counters 2 and 4 also show driving cycles, but then really a "share" of counters 1 and 3, respectively. In principle, counter 4 shows how many times that the customer should have detected symptoms.
Note! For systems with diagnostic concept Generic Global Diagnostics (GGD). If many diagnostic trouble codes are stored at the same time, then certain diagnostic trouble codes (the oldest) will have these frozen values/counters erased, this to save memory in the control module. These diagnostic trouble codes will then only have counter 2 left. Note also that counter 2 will also be erased when the memory is full, but often later than when other counters are erased.
Note! For system with diagnostic concept Volvo Diagnostics II. If many diagnostic trouble codes are stored at the same time, the control module keeps at least half of the oldest and half of the newest diagnostic trouble codes in the trouble code memory.
Note! For diagnostic trouble codes where the malfunction is not detected for many driving cycles and where the malfunction is detected again, then frozen values and counter values are written over with new values, that is, the diagnostic trouble code is considered "new".
Example 1, Intermittent malfunction
1. Counter 1 = 5
2. Counter 2 = 2
3. Counter 3 = 25
4. Counter 4 = 10
5. Driving cycles
After the malfunction has been detected for the first time (driving cycle 0) the malfunction has been detected again in 9 of the first 20 driving cycles (counter 4 = 10). Using this, the conclusion can be drawn that in 11 driving cycles (20-9=11) the test has not been run or the malfunction has not been found, or a combination of these. After the last time that the malfunction was detected (in driving cycle 20), 5 driving cycles have passed (counter 1 = 5), where the test was run in 2 driving cycles without detecting a malfunction (counter 2 = 2).
Conclusion: Intermittent malfunction
Assessment: Good possibility to repeat the malfunction and customer symptom, and thus succeed with troubleshooting, as the malfunction has been found quite recently in several driving cycles.
Example 2, Permanent malfunction
1. Counter 1 = 0
2. Counter 2 = 0
3. Counter 3 = 25
4. Counter 4 = 26
5. Driving cycles
After the malfunction has been detected for the first time (driving cycle 0) the malfunction has been detected again in all following driving cycles (counter 3 = 25, and counter 4=26).
Conclusion: Permanent malfunction
Assessment: Very good possibility to repeat the customer symptom and thus succeed with troubleshooting, as the malfunction has been found in every driving cycle. Since the malfunction has been detected during the present driving cycle (no. 26) it does not really matter for troubleshooting if the malfunction has been detected in all previous driving cycles or not.
The counter show more how "sure" the malfunction is as well as that it can confirm if the customer experienced the malfunction as the counter indicates.
Example 3, Intermittent malfunction
1. Counter 1 = 122
2. Counter 2 = 122
3. Counter 3 = 125
4. Counter 4 = 4
5. Driving cycles
After the malfunction has been detected for the first time (driving cycle 0) the malfunction has been detected again in the 3 following driving cycles (counter 4 = 4). After the last time that the malfunction was detected (in driving cycle 3), 122 driving cycles have passed, where the test has been run in 122 driving cycles without detecting a malfunction.
Conclusion: Intermittent malfunction
Assessment: Not very good chance to repeat the malfunction and the customer symptom and thus succeed with troubleshooting, as the malfunction has only been detected in a few driving cycles a very long time ago.
The less driving cycles a malfunction has been detected in and the greater the number of driving cycles since the malfunction was detected the last time, the more difficult it is expected to be to repeat the malfunction and the customer symptom and thus succeed with troubleshooting.
This can be read off by the lower value is on counter 4 and the higher the value is on counter 1 and 2, as well as the lower the difference is between the value on counter 3 and counter 2, the more difficult it is expected to be to repeat the malfunction and the customer symptom and thus succeed with troubleshooting.
Example 4, Intermittent malfunction
1. Counter 1 = 25
2. Counter 2 = 25
3. Counter 3 = 25
4. Counter 4 = 1
5. Driving cycles
After the malfunction has been detected for the first time (driving cycle 0) (counter 4=1), the malfunction has never been detected again. After the last time that the malfunction was detected, 25 driving cycles have passed, where the test has run in 25 driving cycles without detecting a malfunction.
Conclusion: Intermittent malfunction
Assessment: Not very good chance to repeat the malfunction and the customer symptom and thus succeed with troubleshooting, as the malfunction has only been detected in one driving cycle quite a long time ago.
Example 5 Unknown status
1. Counter 1 = 25
2. Counter 2 = 0
3. Counter 3 = 25
4. Counter 4 = 1
5. Driving cycles
After the malfunction has been detected for the first time (driving cycle 0) (counter 4=1), the malfunction has never been tested and/or detected. After the last time that the malfunction was detected, 25 driving cycles have passed where the test has not been started. Since the diagnostic trouble code test has not started anymore, it cannot be decided if the malfunction exists or not.
Conclusion: Unknown status
Assessment: Read diagnostic trouble code information and try to achieve condition so that the diagnostic trouble code test is started and run, which makes it possible to detect the malfunction. If the malfunction is detected, chances are very good to repeat the customer symptom, and thus succeed with troubleshooting when the malfunction has been found in the current driving cycle.
If the malfunction was not detected even though conditions are fulfilled, then chances are less good to repeat the customer symptom, and thus succeed with troubleshooting as the malfunction has not been found in the current driving cycle.
To decide diagnostic trouble code test's status
By reading out the diagnostic trouble code with associated status identifier, then status for the diagnostic trouble code test (diagnosis) that detects the malfunction and generates the diagnostic trouble code, is obtained.
Example 1, Permanent malfunction
Status identifier:
The diagnostic trouble code test has been run in both current driving cycle and in earlier driving cycles. Malfunction has been detected both in current driving cycle and in previous driving cycle, which indicates that the malfunction is active right now. The control module has requested lighting of the warning light.
Conclusion: Permanent malfunction.
Assessment: Very good chance to repeat the customer symptom and thus succeed with troubleshooting, as the malfunction has been found in current and in previous driving cycle. Since the malfunction has been detected during the present run cycle, it does not really matter for troubleshooting if the malfunction has been detected in all previous driving cycles or not. If this information is supplemented with the counters' values you can decide how "permanent" the malfunction is.
If the vehicle is stationary, e.g., with the ignition on, this means that the test runs directly when the ignition is turned on. This makes it easier to both fins the malfunction and to verify that the malfunction cause has been take care of.
Example 2, Unknown status
Status identifier:
The diagnostic trouble code test has been run in previous run cycles but not in current driving cycle. Malfunction has been detected in previous run cycle, but not in current driving cycle since the test has not started. Warning light is on.
Conclusion: Unknown status
Assessment: Since the test has not started in the current driving cycle it is not possible to decide if the malfunction is "active" right now. First read the diagnostic trouble code information and try to obtain conditions so that the test is started and run, which enables detection of the malfunction. If the malfunction is detected, chances are very good to repeat the customer symptom, and thus succeed with troubleshooting as the malfunction has been found in the current driving cycle.
If the malfunction was not detected even though conditions are fulfilled, then chances are less good to repeat the customer symptom, and thus succeed with troubleshooting as the malfunction has not been found in the current driving cycle.
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 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 adaptation, quick adjustment, bank 1 = 15.63%
- Fuel adaptation, slow adjustment, bank 1 = -0.78%
- Fuel adaptation, quick adjustment, bank 2 = 23.44%
- Fuel adaptation, 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 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.
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.