I have a problem with my Volvo EC240B 81066 It has a intermittent fail to crank fault. Turn the ignition switch, and it bumps the starter, but only for a moment. Holding the key to the crank position makes it hit the starter momentarily, on off on off on off. Likely doesn't get a revolution out of the engine before dropping out, then waits for a second or three, and hits it again momentarily. I had a technician replace the small relay on the starter. The starter has the large heavy power relay, but also has a smaller power relay to energize the heavy relay. Two power relays in series sort of, Anyway, the lighter of the two seemed weak so he replaced it, and it didn't' change anything. The only way to get it to crank is to jumper one of the relays using a length of copper wire, in the same way you would do it in the old days. The ignition lead that should supply power to the start relay on turning the key has solid 24V when you turn the key. But when you actually attach it to the relay terminal, the 24 volts becomes intermittent. and the starter motor starts bumping on off on off like I said. You get a steady fast crank with the jumper wire by hand. Coupled with this problem is a fail to start. We have cranked the living daylights out of this engine and it won't fire either. Smoke from the exhaust and some slight coughing, but no fire. Many weeks ago we fired it up, warmed it up for an hour, then drove it to the fuel tanks to fuel. It got there and died on the spot. Hasn't run since. We have verified it has fuel pressure. Dealer techs are weeks away......HELP!
Check wiring to alternator. Pay particular attention to tiny wires. D+ or W if broken or loose will tell the V-ECU that the engine is running and disallow starting. You also have a crank relay above the batteries on a ledge behind a tin guard. Diode protected. There are 2 diodes flanking that relay. Should be a blue black 2 wire connector that just terminates. Check the diodes. One failed will cause fail to start. Do you have any error codes? Good luck
I should have included, there are no error codes
Then I would proceed as advised BTW, if you put the key in the ignition switch and go straight from off to crank in one motion, will it crank? This is important.
I have mailed but maybe some others may like to have the response. Kind regards Uffex
In reply to the illustration provided by Uffex, I would add that the pic in bottom right corner looks more like terminating resistor behind E series I-ECU. Especially with that part number on it. It should be a small oblong bulbous thing about the size of your fingertip. One on each side of the safety relay. The one that looks like a saucer. Good luck.
Very interesting fault you have there. The alternator is out of the picture as it would not have the rpm and time for the field to saturate and produce voltage at D+. The problem could be a faulty starter safety relay which is the one in yellow on the diagram but i suspect the problem is over on the VECU side. As it and the alternator has the ability to energize that safety relay (which stops the cranking BTW) and it also controls the fuel shut off solenoid which sounds like that is not been energized properly ether. You can try a couple of things to eliminate the safety relay at least. If you short out the two wires in the start circuit on that safety relay and it cranks ok it proves it is that relay or some thing powering it causing the cranking issue. If that works re-connector the wires and remove remove the D+ wire from the alt and the wire in the diagram marked control lock switch from the safety relay. if the issue remains it is the safety relay faulty. If the problem is gone it is over on the VECU side.
I would caution against "shorting " anything on a Volvo. The diodes really don't appreciate it.
If you switch to manual mode it will take the VECU out of the frame. KR Uffex
Switching the computer to manual doesn't change any of the symptoms Thanks for your help, this is helping a lot.
I'm gonna ask again. If you roll the key from dead off straight to crank with no hesitation, does it crank, THIS IS IMPORTANT?
Yes it cranks momentarily. Unlike a pure mechanical moter, it does take a second for the computer to boot, but before thats done, the starter engages, just for a second. Its almost as if something sees revs and quits cranking
Have you checked D+ at the alternator? Disconnect it and ground the wire. See if it cranks
Alternator has large pos and neg leads, plus a 4 pin connector. I unplugged connector. Symptoms unchanged
That is the updated alternator. Does it appear that the harness is spliced in?
No. Ive owned this since near new. Its all factory
Ok, it's a later version than, would be more fair to say. Is your fuse box behind the cab like on a C model?
Yes
Son of a gun. I'll look at diagrams this evening. That's an animal of a different color
Well I looked and I do not have any diagrams or schematics on that particular model that was a late version just before they made the full transition to a C model. The earlier diagram posted up by Uffex Is 4 in early model B series up to the middle generation the later versions which you have are the closest to AC without having fully integrated servo sensors. We'll have to wait until someone who has prosis can provide a diagram or the correct schematic with your serial break
Figure 1 Wiring diagram SCH01 Marking Designation Marking Designation BA3101 Battery 1, (12 V, 200 A) SW3301 Start switch BA3102 Battery 2, (12 V, 200 A) RE3301 Start relay FC01 Fuse, air heater (140 A) RE3101 Main relay 1 FC02 Fuse, main (80 A) RE3202 Main relay 2 FU24 Fuse, start switch MO3301 Starter motor SW3101 Battery disconnect switch AL3201 Alternator RE3201 Resister
Now we're cooking with gas. All your diodes and relays are in the fuse panel behind the cab . Everything in purple is on the circuit board of the fuse panel. I would start by checking RE3301. Maybe swap it out for another for a quick test. If that doesn't get it, look at the pull coil 85 86. With key in run position there should be power on one side ground on the other. I should have asked this early on, does your fuel gauge work? When you go to crank it passes through the relay to the little relay on the side of the solenoid.
circuit with emergency switch Figure 1 Wiring diagram SCH03 HE2301 Water separate heater (option) HE2501 Preheater SW2301 Water separate switch (option) MO3301 Starter motor SW3301 Starter switch MA2504 Internal exhausted gas recirculation SW2701 Engine speed control switch SW9118 Safety lever switch SW2703 Automatic idling switch MA910 Safety solenoid valve SW2704 Emergency switch SE2701 Engine speed sensor - crank RE2501 Preheater relay SE2703 Engine speed sensor - cam shaft RE3301 Starter relay
I have the exact same issue with our John Deere 225 (older unit). I've checked all wiring, test diodes,switches, etc. (all good) Unplug the D+ terminal on alt. Starts fine, but alt light on panel stays on, and hour meter inop. Had to send it out on a job. Waiting for it to come back in for further diagnostics.
Good day The usual way for a alternator fault to show up is that the hour meter will continue to run with the engine stopped and key on. Kind regards Uffex
Check alternator output for A/C voltage. Most likely the diode trio is breaking down.
I find it hard to figure how ac is coming from the D+ terminal. If you all think it is the alternator pull the wire of as a test and see if the problem goes away.
When the diode trio or rectifier craps out, the a/c voltage begins to leak through. It's very obvious with an oscilloscope. And it will be on the U-batt post not D+
Lots of smart people here. Wish I could keep up. Strongco was out, we worked on it for a day. The conclusion is the VECU is shutting the starter off. If I understand it right, the safety relay at the starter is grounded through the VECU. If the computer wishes to prevent the starter from turning, it simply opens the ground on the safety relay. That said, about the only thing that we are seeing is an RPM reading during cranking as high as 4000RPM. So the tech started looking at the engine speed sensors. There is one on the crankshaft, and one on the camshaft, and in theory, the computer should be able to run the engine with either one working. The only way to get the engine to crank normally is to unplug both speed sensors. Of course, without a speed indication, the VECU leaves the fuel off, so no smoke. The Tech ordered a pair of speed sensors and we will try again next week. He is plugged in, but the crank duration is too short for his laptop to register any useful readings while its cranking. It makes it difficult to diagnose for sure. Thanks for all the help. Those diagrams posted look a lot like the ones he showed me on his screen, so he must be on the right track. He was doing all manner of jumping relays etc to overide any faulty component he could. Tested wiring for ground faults, ohms, etc. Speed sensors pass an ohms test, but he needs more complex test gear to really see what they are sending out. I will keep this thread current as info comes in.
Thanks for the feed back watglen. Any chance you can post a close up picture of those two sensors and where they mount on the engine please.
Since I see they are 2 wire speed sensors (reluctance type) you could unplug them so it cranks while having a multi-meter plugged into the sensor set on frequency. Just look for a steady reading while cranking (a little variance will happen as piston runs through compression stroke). If the reading is all over the place you may have a faulty sensor. If you could manage to plug the sensor in and check the same reading at the controller end (may have to pull the wires out of the connector) you should see the same reading there. Different reading then a wiring problem.
Maybe someone can answer my question then, what are they doing counting the teeth on ring gear or camshaft? If his laptop is showing ring gear teeth counts the figure would be close to the truth at cranking speed. The VECU maybe dropping the starter out thinking its time to stop the starter if the sensors are reporting over speed. Alternatively it still could be nothing to do with the speed sensors as the VECU is not detecting some other critical value like oil pressure and removing the sensors is just tricking the VECU to think engine not turning? OR the VECU has gone belly up?
Advise tech to perform active measuring for VECU . Its posted in service side of Prosis. He will be able to see real values without the laptop, but using a breakout box. 4000 rpm cranking? I would pull both sensors and inspect them. Another thing I remembered, another machine similar to yours but a 290. I found the board in between the 2 of the fuse panel had several burnt traces . If you open the fuse box and climb up there and take a sniff, you'll know. All fuses were powered, all diodes were ok. It was an intermittent start as well. I'm not saying that is it, but worth a look.
Well, two new speed sensors and no change. Techs had a 3 way on the phone and its looking like the Engine controller is the issue. Big $$$$ I hope it fixes it.
Did they perform active and passive measuring?
Yes, he was able to see spurious RPM readings during momentary cranking on the laptop.
And was that from the flywheel sensor or the crank sensor. Additionally, was this done with alternator plugged in?
I don't know if he knows which sensor the ECU uses to decide the the engine speed, perhaps both. If he unplugs both, it will crank. If he only unplugs one or the other, it won't crank. He has disconnected the alternator completely, both the heavy battery lead and the 4-pin connector.
Id be really concerned about that high rpm reading. Im not trying to paint a picture of doom n gloom but thete were rare cases of cam failure over near #1 & 2 where the follower would crap out and damage the block. Something to check for
Normally if you have no error code the trouble is mechanical
Just had a thought. Diode 13( the little black and silver fuse looking things) on the bottom of the circuit board/ fuse panel. Have you tried swapping with another? Or if you know how to test them, can you test?
Replaced the Engine control computer and its fixed. Running good and back to normal. Likely have $10,000 on this repair. Ouch! Time to get to work.
Ouch!!! At least she's up n running. Thanks for following up.