Intermittent fault-tracing
Preparations
The reason the car is in the workshop is because the customer has experienced abnormalities with the car. The symptoms experienced by the customer does not always coincide with a permanent fault. The fault might not occur when the customer arrives at the workshop but occurs on a single occasion.
In order to deduce the fault type is important to check the symptoms reported by the customer:
- How does the car behave? Is the car difficult to start, are the gears hard to shift, does the tachometer flicker etc.
- What are the circumstances when the fault occurs? under heavy load, is it dependent on the weather, outside temperature, on uneven roads, when making sharp turns, only when the engine is cold, under hard braking etc.
It is important to interview the customer about the surrounding circumstances in the event of a fault.
It may be an advantage to simulate the driving conditions for when the symptom occurs and carry out an analysis and deduce the fault. By deducing the fault, the symptom can be remedied so that the fault does not recur.
When a diagnostic trouble code (DTC) has been stored the freeze frames are also stored. These can be used to recreate the driving conditions for the diagnostic trouble code (DTC).
Tools:
- Reading off freeze frames, read off the freeze frame data for the relevant diagnostic trouble code (DTC)
- Status identifier, read off the status of the selected diagnostic trouble code (DTC)
- The counter indicates, amongst other things, how many fault free cycles have been carried out since the diagnostic trouble code (DTC) was stored.
Intermittent electrical fault
An intermittent electrical fault can be caused by faults in the wiring, components or connectors.
Possible fault causes for intermittent electrical faults are:
- Damaged terminal pins in the connector
- Loose connections in the connectors
- Poor ground connection (oxidation)
- Moisture, poor connections in the connector
- Defects, cracking, damage on the components
- Strong magnetic or other interference that has affected the control modules.
Intermittent functional faults
Intermittent functional faults could be caused by mechanical defects in the components.
- Cracked or blocked hoses
- Incorrect oils, fluids
- Incorrect fuel
- Sticking mechanical components.
Intermittent internal faults
Intermittent internal faults could be due to:
- Electromechanical interference
- Power supply too low
- Oxidized ground terminal for the control module
- Defective internal components.
Intermittent communication problems
Intermittent communication problems could be due to:
- Electromechanical interference
- Oxidation / loose connections in the connectors
- Defective signal cables.
Simulating fault causes
A large amount of input data is a required to recreate and simulate fault occurring circumstances.
Certain cases can be difficult to recreate. High speed driving and stalling to achieve high loads is not recommended.
In order to achieve high loads accelerate hard in quick succession a number of time instead.
Cases that are possible to simulate:
- high load
- moisture
- heat
- cold
- loose connections.
High load
High load can be simulated by accelerating hard repeatedly.
Moisture
Moisture can be simulated by spraying water on the suspected faulty component or connector using a spray bottle or hose.
Heat
Heat can be simulated by using a hot air gun or similar to heat up a suspected faulty component or connector.
In order to achieve a high engine temperature allow the engine to idle at a high load with the hood down to prevent air flowing through the engine compartment. Run the engine in hot conditions. Read off the engine coolant temperature (ECT) using VIDA (Volvo scan tool), the temperature gauge in the combined instrument panel is progressive.
Cold
Cold can be simulated by cooling down the suspected faulty component or connector using a freeze spray.
Loose connections
Loose connections can be simulated by twisting and shaking the connector while the function is activated.