Diesel no starts: the new rules

March 1, 2016
Diagnosing and repairing diesel no-starts can be very profitable if you know what to look for. The rules have changed in the last few years so it pays to know what to expect on a newer diesel vehicle with a no-start condition.

Diagnosing and repairing diesel no-starts can be very profitable if you know what to look for. The rules have changed in the last few years, so it pays to know what to expect on a newer diesel vehicle with a no-start condition.

In fact, the process is much like diagnosing a no-start condition on any other type of vehicle – begin by performing a good preliminary inspection to catch anything obvious, check for service bulletins, tips and programming updates, and then (using service information) develop a theory about what’s happening, observe and take measurements to prove your suspicions are indeed correct, and then fix the problem.

It's easy enough in theory, but as with any other system, it helps to know what you’re checking, and what to watch for, so you don’t waste diagnostic time or miss something obvious.

Diesel fuel control systems have changed drastically in the last few years (even among similar vehicles from the same manufacturer), so it’s really important to understand how the system works for the exact model, engine, and year of vehicle you’re working on and not just have a general overview of a generic system. There are actually two reasons to be so specific and precise.

  1. High-pressure diesel systems do indeed run at extremely high pressures, so it’s important to know the oil and fuel pressures expected at each part of the system and to be ready to test them safely, without ending up in the hospital or maybe even worse.
  2. Understanding why each diagnostic step in the procedure is performed, and exactly what to look for while doing it can often be the difference between a quick, accurate diagnosis and a long, expensive drawn-out headache.

If you’re ready to take on the challenges, here are a few tips for quickly diagnosing no-start conditions on newer diesel vehicles. We’ve learned them the hard way, so you won’t have to.

Preliminary checks on diesel no starts

Preliminary inspections are really important on diesel vehicles because they can save so much time and because so many no-start conditions can be accurately diagnosed and repaired in the early stages.

After verifying the problem, start by opening the hood and climbing up if necessary, and then checking that the battery cables and connections are clean, tight, and secure. Check that the starting system connections and relays are securely in place and check that the glow plug and glow plug control module connectors are okay as well. It’s not uncommon to find one of these connectors has wiggled out of place or is compromised in some way.

Here’s a tip: if you do suspect a fuse or wiring problem, quickly checking to see if anything else isn’t working and then finding out if those systems share a common fuse, splice, or relay can save quite a bit of diagnostic time. It’s also very common on diesel trucks to find that accessories have been poorly wired into the circuits that supply power to the starting and fuel injection systems. When the fuse protecting the circuit blows, the vehicle subsequently won’t start, so it’s important to identify where those fuses are and then check them carefully early on in the diagnostic inspection, especially if the no-start problem just suddenly happened one morning.

Since high-pressure diesel fuel injection systems rely on a consistent stream of high-pressure engine oil to operate the fuel injection systems, engine oil condition and level are critical and anything that would affect this is worth noting. While under the hood, pull out the dipstick and inspect not only that the oil level is okay (way over full may indicate fuel or coolant leaking into the engine) but also actually sniff the oil for contaminants to help identify any problems. Be careful though, the dipsticks do tend to fray, and the wires can stab your fingers.

Be suspicious if the oil looks like it was just changed – cheap oil changes are sometimes really expensive in the long run since using the wrong viscosity oil can cause a no-start condition. Also note any oil-soaked harnesses or connectors, which may be a symptom of the larger problem in the high-pressure oil supply system that should be investigated.

When the underhood checks are complete, turn the key on (engine off) and listen for the noise as the fuel pump turns on for a few seconds and pressurizes the system. Also watch the instrument cluster to ensure the Check Engine light comes on during bulb check and check that the “Water in Fuel” light isn’t staying on (though, to be fair, faulty sensors are not uncommon). Any of these situations indicate larger problems ahead that you’ll want to be aware of.

Be sure to check the transmission range switch. Even wiggle the shifter and see if the vehicle starts up. One of our customers has a fleet of Ford pickup trucks that often get mud build up around the transmission range switch, which stops the switch from going to park (and thus won’t start after it’s shut off). Cleaning away the mud fixes the problem quickly.

Another part of the preliminary checks is to verify power and ground at the fuel pump, fuel pressure at the fuel pump and the rail (using the correct tools, gauge, and service information), and make sure there are no obvious restrictions in the intake or exhaust systems – which can happen if the vehicle spends most of its life idling or is often driven at low speeds. Don’t just rely on the gauge on the side of the air cleaner box. Remove the element and actually check for restrictions to be sure.

Make sure none of the “override” switches have been tripped and make sure there’s fuel in the tank. Resetting the switch or priming the fuel system may be all that’s needed to fix the problem.

The most common problems and fixes

If the vehicle won’t crank, from experience, the most common cause of the problem on diesel vehicles is a weak battery, especially if the vehicle was parked in the cold overnight, but that doesn’t mean just dropping in a new battery and sending the vehicle on its way. That’s asking for trouble.

From experience, in these cases, it’s good practice to charge and check all of the vehicle’s batteries, as well as the charging system, and make sure the block heater and cord are okay. Finally, ensure that nothing was left on to drain the battery before releasing the vehicle back to the customer. Fixing the same problem twice is embarrassing and costly.

One interesting note is that a battery doesn’t need to be all that weak to cause starting problems. Many no-start diagnostic trouble charts state that both batteries must be charged to at least 12V, and they’re not kidding around. Anything even slightly less than that may cause problems. In fact, batteries that are slightly discharged but still as high as 12V can and do result in no-start conditions.

One excellent dealer tech says he’s seen some newer Ford diesel engines make a disturbing clanging sound as the vehicle tries to start with a battery that’s not quite fully charged but still at nearly 12V exactly, and that charging the battery a bit – or even just plugging in the heater for a few minutes stops this problem (along with a proper charging system check, of course).

This isn’t meant to be a substitute for proper diagnosis: Always check service information and follow the recommended diagnostic procedures but keeping in mind that tolerances on high-pressure diesel fuel systems are pretty strict can save diagnostic time. “Just about” 12V isn’t the same as “at least” 12V when diagnosing these vehicles.

If the batteries and charging systems are indeed okay, it’s good practice to “check the basics,” meaning making sure the starter is okay, including testing for voltage drop on the cables and checking for power at the starter relay, checking that the glow plugs are ok, and the glow plug control module operates (including verifying power and ground), and checking for power to the fuel pump circuit. If the vehicle cranks fine but starts and quits (“no start” means different things to different customers), watching the exhaust pressure during cranking can help locate a plugged exhaust. If it gets high fast, the exhaust may be indeed plugged. Most of the time these preliminary checks will give you a good idea of what’s causing the problem by now, but there are vehicles that need a bit more testing.

Electrical problems

Even though the diagnostic charts usually direct you to check fuel quality right away, from experience, checking for Diagnostic Trouble Codes (DTCs) and programming updates early on in the diagnosis is a smart move that can really save diagnostic time. In my own experience, I’ve seen far more problems solved by hooking up the scan tool early on and investigating the parameters, programming versions, and DTCs than by immediately sampling the fuel quality (not that that doesn’t happen and isn’t a valuable check).

Finding out if any codes relating to the fuel injectors, control sensors, or modules are stored really doesn’t take long at all and leaves you smelling much better than sampling the fuel will.

If DTCs related to those systems are present, taking a few minutes to record and investigate them is smart since they’re probably related to the no-start condition, and since a surprisingly large number of no-start conditions are fixed by reprogramming a module, it’s also wise to check for calibration in the modules’ updates early on. This can and does save time and headaches.

Additionally, it’s a good idea to watch what’s actually happening to the critical inputs on the scan tool before and during cranking, checking for not only the presence and value of the critical parameters (to make sure the engine has the correct parameters to start and run), but also to note any that disappear, change drastically, or disappear during cranking. Service information will list the critical ones along with expected values, which can save hours of time later on. From experience, a problem in the electrical system tends to fail suddenly rather than develop slowly and get worse, so if the problem developed suddenly, pay extra attention when observing the reading (especially if you noticed oil-soaked harnesses or leaks earlier on).

Again, following service information is important, but it’s also important to understand what you’re looking for and why, so you don’t waste time or miss the obvious symptoms.

Glow plugs

As much as diesel systems have changed and evolved, faulty glow plugs are still a common problem that causes no-start conditions. Fortunately, on newer vehicles, the systems can set trouble codes to indicate problems and save diagnostic time.

If the no-start problem occurs when the vehicle is cold, or if the vehicle has been getting harder to start when it’s cold, checking the glow plugs early on in the diagnosis is a good idea. The Ford dealer tech mentioned earlier quickly checks glow plug values (resistance and amperage draw) during regular services to catch them and replace them before they cause a no-start condition.

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 okay. 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.

Fuel quality

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 (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 causes 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. That won’t likely change any time soon.

About the Author

Vanessa Attwell

Vanessa Attwell is a Master Technician for two major manufacturers and has also worked on the bench of an independent shop. She has developed and delivered training for both vehicle manufacturers and independents, and helped develop government training and regulations standards. She drinks too much coffee and spends her spare time sitting in traffic.

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