Hello, and thanks for checking out this post on a Sprinter intermittent no start, no crank issue. The vehicle in question this time is a high-mileage Sprinter delivery route truck with a diesel engine. The problem cropped up with no apparent pattern, failing to crank at random times, and would often go some time with no problem. The starter and alternator had already been changed with no effect on the issue, and had been to the shop several times without success in replicating the problem. Finally, it was towed in after a complete failure.
Another mechanic started to look at the vehicle and was now able to reproduce the no crank several times. Oddly, when a no crank event happened, the electric A/C fan would run at key on, then nothing would happen when the key was further turned to start. I am always a little concerned about complaints of starting issues on Sprinters; if the first crank attempt fails to start the engine, the key has to be turned back off before trying to crank again. This seems to be common on foreign vehicles, and may trip some people up. However, the fleet that owns this Sprinter also has several others, so driver knowledge shouldn't be a problem. The starter relay is located behind the access panel under the driver seat. If you hold onto a starter relay and turn the key to start, you can feel the relay click when it energizes. That doesn't mean it is necessarily putting out power, but you know it has power and ground to energize it. This one was not clicking during a no crank, so the problem had to be between the key switch and the relay.
At this point the other tech's shift ended and it was my turn to take a stab at the problem. With the knowledge of what part of the circuit to look at for the issue, I looked at the wiring diagrams the other tech had printed from Mitchell. I was looking at the wiring for some commonality between the starting circuit and the HVAC fan, when my shift manager came up with a diagram isolating the starting circuit. It was obvious that a couple of connections in that circuit were worth looking into. Particularly suspicious was a connection above the fuse block, and a splice joint below the seat. The engine control module itself was also worth thinking about.
Below is a condensed version of the starting circuit. There are several things I find a little strange about how the circuit is wired. First, the starter relay gets power off the ignition switch itself. Normally a relay is powered from the battery so that reliable, high amperage power is available to the starter solenoid. The power from the switch signals the ECM to send ground to the starter relay to energize it. Also, the module pin marked starter motor relay +12V supply really isn't relay supply, but only power to energize the relay. It also energizes the fuel pump relay, which is not shown in my diagram. I understand that it is desirable to control the starter relay through the ECM, but the way this is wired, the starter solenoid is in reality getting its power directly from the 12GA wire from the ignition switch! The solenoid power also has to go through 4 connectors on its way to the starter. This seems to me to be a rather unreliable way to wire a starter circuit, as each of these connectors is a potential problem spot, especially as a vehicle ages. So much for the myth of fine German engineering.
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| 2005 Sprinter starter circuit |
Anyway, the fuse block under the steering column is easy to remove, so this seemed like a good place to start. Dropping the fuse block from the column caused the no crank issue to reappear, so it seemed as if one of the connectors there was at fault. The 12GA black/yellow wire from the switch goes to a connector at the right side of the block, and it re-emerges at another connector on the left side of the block as a 10GA violet wire. I jumped a wire between the two and the vehicle started. There is probably a fusible link across the top of the fuse block to protect the switch wire, but I had no desire to take the block apart and spend the next 2 hours chasing small parts across the shop just to find out. I cut the two wires off at their respective connectors and soldered them together, then bolted the fuse block back up.
I wanted to also check the starter relay under the driver seat to make sure its connector was sound. I grabbed the wires near the connector and pulled with about 10 pound of force, while trying the starter. The vehicle failed to start as long as I pulled on the wires. This is a sure sign that the connectors in the relay plug have lost their tension and can cause an intermittent fault. The OEM relay has 2 large spades that I didn't have a connector for, so I wired in a standard 5 blade relay with new terminals.
The last thing I wanted to check out was the splice in the violet wire the diagram said was under the driver seat, but it was not there. There is a fork in the harness under the vehicle, (under the seat area) so I assume that is where it is. I didn't break into that as it was in original condition, well-wrapped, and I didn't want to disturb it since I was pretty confident the problem had been solved.
It has been over a month since repair and the vehicle is driven daily, so it looks as if one or both of the things I did fixed the problem. As to why the HVAC fan ran when the truck failed to start, I haven't really come to a conclusion as to the answer. It may be a quirk in the input/output circuits or programming of the ECM. One of these days we will replace a bad fuse block in one of these and I can blow it apart and check the guts, but one may want to insert a piece of fusible link wire between the wires I soldered together so the switch doesn't burn up in the event of a short or an overload in the starter circuit.
Thanks for checking out this post, and check back soon for more.
Bruce
Source: https://thetruckmechanictoolbox.blogspot.com/2013/01/2005-sprinter-no-crank-no-start.html
Posted by: stevenpressessidowoad.blogspot.com
