Cat wheel bumcher JCB00321. No crank from key switch. Operator has been jumping the solonoid at the starter with key switch for some time. Checked the key switch first and it is putting out voltage I'm start position. So I got.the wiring diagram to attempt to locate the starter relay. According to wiring diagram the is no starter relay. Wire 306-A82 GN-18 pin 65 on ecu is key switch input to ECU. Checked voltage at ecu pin 65 key in start and have 24V. So then I check wire 306-A83 pin 20 ecu. It shows going directly to the starter solonoid. Found open circuit open on this wire. Repaired open circuit . Still no crank from key found found 13v constantly to starter and have voltage low at start solonoid code. ecu is damaged from crossing started ? Should I replace starter at the same time just for piece of mind with the new ecu? It is odd to me there is no external relay.
A lot of equipment has the ground to the starter solenoid 'controlled' by a diode in the alternator.... ie. if the alternator is producing voltage(running) it does not give a ground to the solenoid even though you have sent voltage to the solenoid to tell it to start. It's a protection from cranking when running... you may need a new alternator... I don't know if cat's works this way or not however
Before changing the ECM I would check the solenoid coils. A shorted pull in coil will pull the voltage down .The ECM will be current limited .if you have a spare starter or similar solonoid just connect the solenoid and try
The starter signal wire has 13v any time the key switch is on. Pin 20. Even if disconnect from starter. I will replace the starter first as I planned to replace anyway.
I rechecked the voltage on the signal wire. In run with the wire hooked to the solonoid I have 0 volts then when in strart I get the voltage low code. Customer is going to get a replacement starter. Mark250 thanks for the sound advice. I guess that 13v is just the ecu voltage to identify the circuit.
A lot of cat circuits use pull up or pull down resistors which impose a small voltage in the circuit for troubleshooting and diagnostic purposes
I replaced the starter with after market, which is what was all ready on it when I got to this machine. Replacing the starter made no difference . The code is 677 fmi 5. With every thing hooked I have no voltage from pin 20 to the start solonoid. The ground wire at the start solonoid appears to be connected to frame ground in the schematics and is continent to frame ground on the machine. ??? Don't want to buy the Ecu and the cat service call and find out it is something else.
I think I figured it out, will not know for for sure until tomorrow. It has been staring me right in the face the whole time. The signal wire pin 20 is hooked up directly to the start solonoid on the starter. I believe the current generated by the ecm is not enough to pull that big throw relay. There is supposed to be a small relay on the starter. Neither the first starter I encountered or the new had one. Customer said when he went to starter shop he told him he want one just like this one , so they took the new relay off the new starter . Anyway no telling how many times I had my finger on it and followed the 306 wire right off the relay, even though it was odd it did not have a relay.
Ronsii is correct in that relay is a safety relay that prevents the starter from engaging while the engine is running. Track the diagram back from that point to the source and see if it is the alternator or a diode.
I will definitely check that out when I get the circuit proper.
Wire 306-A83 was hooked directly to the post marked S in the previous picture .
I never did like Cat schematics!
Installed the relay, no change. Get 677 5 code just by turning the key switch to the on position. I think I am going to work on something else for a while. The ground is present at the relay in regards to the question about the alternator relay.
Cannot see the current codes in the log list guess it is full
And I thought I had it bad when somebody brings me something with a dozen different errors.
Got it going, talked to cat rep. He tells me schematic is wrong says the voltage from key switch goes directly to relay and the ECU is after the fact. Replaced the wire I had repaired that showed open circuit back to original and that did it, along with the relay. Thanks ,on the drive motor leaking into the transmission gearbox.
What version of the schematic do you have.? Currently on CHG02. Ref. KENR7576-02 dated Jan 2018. If you need it let me know and I'll PM it to you.
I had a quick look at the schematic for your machine and it makes sense to me. Wire from key switch goes to ECU and ECU then signals the starter relay at the appropriate time. If you've wired the key switch directly to the starter relay then you've bypassed any safety interlocks that were the job of the ECU. I advise caution.
This rambling saga I posted may have been missing some information. I have not bypassed anything in the end. Ecu pin 20 shows going to the starter relay in the schematics. When I first checked that wire , it showed an open circuit according to the schematic. The starter relay is actually mounted on the starter itself. This relay was missing when I first encountered this machine. So I " corrected" the open circuit from pin 20 to the start relay and installed a new relay. Still would not start from key switch. So then I corrected my " correction " back to the way it was originally wired with factory harness and that solved the issue. Big ass circle I made all because the relay was not in the machine when it arrived. So the description of the wire going directly to the relay may or may not be accurate but with harness " as shipped "it works correctly.
Nige, that is the version I have. On a side note I have recently discovered that my CAT dealer will print these schematics on a map size paper for a reasonable price and they are so much easier to follow to me than on the computer screen.
I assume you have a local copy/print shop somewhere close by. Have you asked them.? Probably be cheaper than the Cat dealer.
$25 plus tax.
Even highwaymen had the decency to wear a mask....
I email those prints to Kinko/Fed Ex and have them printed on 24"X36". They are usually done in20 minutes or less for around $28.00.
For color that’s a good price I was quoted $50 to print schematics a couple years ago in color I used to get B&W ones done for $5 a sheet at Staples but I haven’t had to do them in a couple years