To solve the “Click no start” problem we need to divide into groups of problems.
The first group could be the Battery and Charging System.
The second group could be Security and Relays.
The third group could be the Starter and its Solenoid.
Initial Testing
To find out which group you have, test by turning on the interior light , turn the key if the light goes out it is the first group Battery and Charging system.
If the light stays on, next test by running a wire from the small terminal on the starter.
To do this you should make up a test lead. Get a 2m or 8 feet length of hook-up wire. Connect a small alligator clip to each end. Connect one clip to the small terminal on the starter and the other end to a multimeter lead. The other meter lead must go to earth (ground/negative). The seat mounting bolts are a good earth.
With the meter resting on the seat and switched to 20 volts DC, turn the key. If the meter reads 12 volts you have good security (SKREEM) and relays circuit so go to the third group. If you do not get the 12 volts the problem is in the second group, Security and Relays.
Background information.
Most electrical problems are caused by poor electrical connections. To understand why we need some basic science.
All metals except gold oxidize when exposed to moisture. Oxides are good insulators. MB uses good quality connectors with rubber seals but a little bit of moisture still gets in. The more important pins are silver plated. If a plug has provision for 6 wires but only has 5 fitted then there should be a rubber plug in the 6th hole to keep moisture out. Mixing metals for connections makes things worse. Cheap pins are tin pated steel, better ones are tin plated brass, the next up is plated silver. The best are gold plated.
If something is not working there is a good chance it is not properly connected to the loom. If you have a bad connection the ECU cannot see the device and chucks a code. If you then scan the vehicle you will get a message like XYZ is faulty when in fact it is not, but is just not connected.
Things like relays are hard to keep free of moisture so they are placed under seats or in closed boxes.
High current circuits have an added problem. A small amount of oxide causes some resistance this resistance causes the connection to get hot which greatly accelerates oxidation. This is very noticeable on battery terminals. When a heavy cable with a copper crimp is bolted to steel, because you have mixed metals you get oxide problems.
This is common when a negative battery cable is earthed. All is not lost if you keep moisture out with some form of moisture barrier like lanolin or silicone. If the oxidization occurs inside a crimp you can remove the oxide with something like soldering flux, the function of fluxes is to get in under oxide layers. If you clean a crimp with flux you must then wash and dry it quickly then soft solder it. Washing your engine with water is a sure way of generating many faults. Using a steam cleaner on any modern engine can lead to a very big repair job.
Battery and Charging System
If you have a problem in the first group you must decide if the battery is flat or there is a cable problem.
To test the battery connect a multimeter directly to the battery terminals it will normally show 12.6 volts. Get someone to turn the key. If the battery voltage drops to say 9 volts then your battery is not charged. If the voltage stays up around 12 then you have a cable problem.
To find the cable problem place one meter lead on the negative terminal and the other lead on a shiny metal part of the engine, turn the key again, if the meter reads less than 1 volt your battery earth is OK if it reads say 4 volts then your earth cable is the problem.
If your battery earth is good then test the positive terminal connection. To do this place one lead on the positive terminal directly and the other lead on the copper lug of the heavy wire. With key on, once again if it reads less than 1 volt you are Ok if it reads more your positive terminal is corroded.
By now you know if it’s the battery or the cables. If the battery is flat then we have to decide if it’s a faulty battery or a charging problem.
A common problem with Sprinters is the cable that connects the alternator to the battery. To test this it is best to get the engine running, so best to charge up the battery with a good 3 stage charger. If you only have an old style battery charger then it is prudent to disconnect the earth terminal on the battery to charge it by connecting directly to the terminals.
Once you have it charged and reconnected, start the engine. To decide if it is charging the battery use your multimeter to measure the battery voltage, it should be above 12.6 and slowly rising. A bit of fast idling should bring the voltage up to over 13volts. If this voltage is not rising over 12.6 [or less] then you may have a potential cable problem.
To test this connect your multimeter to the large terminal on the alternator. While the engine is running, with the voltmeter negative lead earthed your meter may show the same voltage as the battery. If it does you have an alternator problem. If the voltage at the large connection of the alternator is more like 14 volts then you have a cable problem.
If you have a cable problem then remove the earth lead on the battery first (for safety), then remove the cable. When you have the cable out, look for discolouration of the wire going into the crimps. If you find that, repair as in the discussion of corrosion above. Note there can be a heavy fuse in the cable under the engine, this is unlikely to be blown but it could be corroded.
At this stage we should consider the glow plugs. If when you turn the key the glow plugs come on it tells us that the ECU is happy for the engine to start but the start relay is not being energized. If we keep trying to find the fault turning the key many times then we risk flattening the battery because the glow plugs draw a lot of power. We are also shortening the life of the glow plugs by constantly heating them. If you have this situation it is best to unplug the glow plug controller, if you can find the glow plug fuse then pull it. If you are not able to find the fuse you can unplug the small 4 pin plug that connects the controller to the ECU.
Security and Relays
If the problem is in the second group then we have to work through the cct [aka circuit] to find the cause.
The starting circuit is complex for safety and security. The way it works is to first establish if you have a valid key. that verified, it checks to see if the transmission is in neutral, then the ECU checks if the basic parameters of the engine are safe to start. If all that is OK then the start relay is energized.
If you can find your start relay using the excellent information that is posted on this forum then you can feel the relay to find out if it is being energized.
Fuse Block #2 Fuse Map 2004
https://sprinter-source.com/forum/showthread.php?t=24683
If it’s not or you are not sure, pull the relay out and look at the pins, if they are clean and shiny then we have to look at the voltages on the pins in the relay socket. Pin 30 should have 12 volts, pin 87 is the lead to the starter and will show 0 volts. The other pins 85 and 86 will have voltage across them when the ECU is trying to start. To verify this place your meter leads in 85and 86 turn the key. If you get nothing then the ECU is not telling the relay to start. If you get volts when the key is turned then the relay is being energized but is not sending the voltage to the starter, this could be a faulty relay or the wire to the starter is open.
Starter and its Solenoid
If the starter is faulty we need to pull it out and test it. Never ever short out the big terminals it is dangerous and proves nothing. The other thing to never ever do is hit the starter with a hammer. This practice started in the days of crude stator wiring, The modern starter has a permanent magnet stator that is made from very strong rare earth magnets these magnets are reliable but brittle. Eric.
