Jcb 416HT can bus fault

[3cpowertrain]

Hi Can anyone help me with a JCB 416HT she died and we have a can bus light on.. she turns over but start is inhibited.. I have checked through all the wiring and voltages and carried out a resistance test on the high and low can bus wires all seems good.. any suggestions would be appreciated.. I can’t get jcb out as they aren’t doing site visits due to the current situation

 

[njneer]

Why results did you get from your tests , voltages and resistance ?

 

[# Robin]

Have you got any error codes up?
Like you my first instinct with a Can error is an ecu offline due to power fault (engine ecu
or acc pedal). When did it stop working?
What age machine is she?
cheers

 

[Timbo]

What resistance have you got on CAN H&L wiring with all control units plugged in ?

 

[3cpowertrain]

Thanks for all replies..
I have 118 amps down each wire between the ems dash and the ecu when plugged in.
The voltage on the high wire does seem to drop down by 2 volts when plugged in!! There are no error codes at all which is throwing the situation..
according to the manual the can bus should only come on when there is a fault between the ZF computer and the ems dash.
I do have two points of concern.
1, there is a plug off of the can bus loom under the dash which isn’t plugged in or capped off I can’t seem to find it on the wiring diagram very close to it is the make part of the plug??!! I have tried to plug this in as there was no dust or anything in the plugs suggesting they weren’t plugged!! When its plugged the ems then reads a trans temp fault trans temp bad and all temp gauges flash!! And code ZF54 comes up..
2. the battery light wire on the alternator only reads 1.8 volts when connected to the alternator but 22 volts when off of the alternator which suggests and connection fault somewhere.. I have checked this wire again on the plug on the ems and it’s the same there..all feeds to the emsdash are correct..
I’m thinking if it the ems dash at fault..
Does anyone know what the fuses are on the fuse / relay board under the cab I know it’s a 12-24 converter and it runs the ecu just unsure what fuse and relay does what..
thanks again..

 

[Timbo]

Thanks for all replies..
I have 118 amps down each wire between the ems dash and the ecu when plugged in.
The voltage on the high wire does seem to drop down by 2 volts when plugged in!! There are no error codes at all which is throwing the situation..
according to the manual the can bus should only come on when there is a fault between the ZF computer and the ems dash.
I do have two points of concern.
1, there is a plug off of the can bus loom under the dash which isn’t plugged in or capped off I can’t seem to find it on the wiring diagram very close to it is the make part of the plug??!! I have tried to plug this in as there was no dust or anything in the plugs suggesting they weren’t plugged!! When its plugged the ems then reads a trans temp fault trans temp bad and all temp gauges flash!! And code ZF54 comes up..
2. the battery light wire on the alternator only reads 1.8 volts when connected to the alternator but 22 volts when off of the alternator which suggests and connection fault somewhere.. I have checked this wire again on the plug on the ems and it’s the same there..all feeds to the emsdash are correct..
I’m thinking if it the ems dash at fault..
Does anyone know what the fuses are on the fuse / relay board under the cab I know it’s a 12-24 converter and it runs the ecu just unsure what fuse and relay does what..
thanks again..

So 120ohms is correct on the can wires - you have all modules and the terminating resistors correct and in circuit. Disconnect one and you should have 60 ohms as a test. Without an oscilloscope you should have approx 4v and 2 v on the can wires with the ignition turned on. Presume you have checked both can lines for shorts to ground also??

Have you got a 'scope? Can tell a huge amount of whats going on the network if you have.

Without a scope, the next thing is to double check all modules are powering up, but if one was missing on the network (i.e. no power) you would have a bunch of no communication codes - but double check all the same.

I always keep some 60 ohm resistors to pop in the can line with a module disconnected to rule out module faults - in your case if you put a resistor in the Dash connector the engine should then start if it were faulty.

Hope this helps abit, but sounds maybe next stage is dealer and look at some live data.

 

[njneer]

Thanks for all replies..
I have 118 amps down each wire between the ems dash and the ecu when plugged in.
The voltage on the high wire does seem to drop down by 2 volts when plugged in!! There are no error codes at all which is throwing the situation..
according to the manual the can bus should only come on when there is a fault between the ZF computer and the ems dash.
I do have two points of concern.
1, there is a plug off of the can bus loom under the dash which isn’t plugged in or capped off I can’t seem to find it on the wiring diagram very close to it is the make part of the plug??!! I have tried to plug this in as there was no dust or anything in the plugs suggesting they weren’t plugged!! When its plugged the ems then reads a trans temp fault trans temp bad and all temp gauges flash!! And code ZF54 comes up..
2. the battery light wire on the alternator only reads 1.8 volts when connected to the alternator but 22 volts when off of the alternator which suggests and connection fault somewhere.. I have checked this wire again on the plug on the ems and it’s the same there..all feeds to the emsdash are correct..
I’m thinking if it the ems dash at fault..
Does anyone know what the fuses are on the fuse / relay board under the cab I know it’s a 12-24 converter and it runs the ecu just unsure what fuse and relay does what..
thanks again..

Your alternator may be the problem .
connect Your test light earth clamp to the positive terminal on the alternator and touch the terminal for the battery light if it doesn’t light the test light then the alternator is faulty.
Disconnect the alternator light wire and earth it and see if it starts.
If the alternator has failed internallly and is not earthing when stopped to put the light on , the ecu
May think that the engine is still running and has latched the interlock to stop you trying to start it with the engine already running .

 

[Timbo]

Your alternator may be the problem .
connect Your test light earth clamp to the positive terminal on the alternator and touch the terminal for the battery light if it doesn’t light the test light then the alternator is faulty.
Disconnect the alternator light wire and earth it and see if it starts.
If the alternator has failed internallly and is not earthing when stopped to put the light on , the ecu
May think that the engine is still running and has latched the interlock to stop you trying to start it with the engine already running .

That's ^^^^^ also a good call.

 

[Wombat]

Most passive Can terminators are 120ohm and you get 60 when both end of the bus are correctly terminated

 

[Timbo]

60 ohms between can and earth yes. 120 ohms between the two cans

 

[jimmystew]

hi there, i have the same problem and just wondering what your out come was with any help appreciated. thanks