Use service information before testing anything, checking that the connectors are good and they all draw about the same amount and that the relay’s connections are secure – and of course that power and ground are OK. This doesn’t take long and can pay off. Water has been known to get into the connectors and damage the connector and module.
Times may change, but faulty glow plugs and their control circuits still can and do cause no-start conditions.
From experience, fuel-related problems do tend to develop slowly and get worse over time, but problems that develop immediately after a fill up may very well be related to bad fuel – and hopefully not a full tank of it. If the gas looks or smells “off” or the customer admits they filled up at a less reliable source, be suspicious.
If you do suspect poor quality fuel (or the incorrect fuel, which still happens) consult service information to find out the correct procedures to drain and repair the system. Sadly, there’s isn’t an easy way around this – newer diesel vehicles need good quality fuel to start and run properly and the cheap stuff can cause problems.
Diagnosing and repairing diesel no starts seems complicated, but in reality it’s often straightforward and relatively simple – if you know what you’re looking for and you do the research ahead of time.
Diagnosing the systems involves reviewing service information (including TSBs and programming updates) to understand the exact system involved, develop theories about what’s causing the problem and then proving or disproving those theories by taking measurements and making observations – and on newer diesel systems, it’s really important to understand the purpose behind the diagnostic steps being performed and know what you’re looking for so that you don’t waste valuable time. Blindly following a generic chart without understanding what’s being tested and why cause needless headaches.
When diagnosing problems, it pays to be prepared and to keep in mind what you’re doing and what you expect to see to keep diagnosis quick and profitable. And that won’t likely change any time soon.