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Super Weird Fault "Overheat"

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Super Weird Fault "Overheat"

Postby Cretosx » Sun Jan 23, 2022 5:01 pm

Hi all, long time lurker here

I've got a MK6 transit RWD 2.4 TDDI, and its got a fault that has absolutely mind boggled me and i'm basically at the point of begging for help.


I was driving down the motorway and I noticed the temp gauge shoot well into the red and thats where it stayed, upon inspection I felt the engine was barely warm too the touch, the engine then shut down and wouldn't restart so I got it towed and went back a week later, and too my surprise the temp gauge is still in the red engine turns over but no start, I replaced the "CHT" sensor but there has been no change.


So if anyone has any input it would be greatly appreciated!
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Re: Super Weird Fault "Overheat"

Postby knobby1 » Mon Jan 24, 2022 12:35 am

Have you checked the CHT wiring connector and loom all the way back to the PCM...?? They can break in the sheathing and cause issues....a continuity test will verify if it's ok.

Lord Knobrot
2008 2.4L RWD 170+PS 6-speed 350 LWB High Roof.

When I die, I want to go peacefully in my sleep like my Grandfather, not screaming like the passengers in his car..!
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Re: Super Weird Fault "Overheat"

Postby Cretosx » Mon Jan 24, 2022 2:46 am

knobby1 wrote:Have you checked the CHT wiring connector and loom all the way back to the PCM...?? They can break in the sheathing and cause issues....a continuity test will verify if it's ok.

Lord Knobrot


Hi sorry my thread didn’t come up, had no intention of spamming! Did look to remove them, the cht wiring looks fine is receiving voltage too, it’s weird that it’s pinned with absolutely no battery connected and no ignition but it doesn’t seem stuck, the engine will not turn over at all unless the fans are on max it won’t start though regardless, cheers for the suggestion.
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Re: Super Weird Fault "Overheat"

Postby knobby1 » Mon Jan 24, 2022 3:45 am

Cretosx wrote:
knobby1 wrote:Have you checked the CHT wiring connector and loom all the way back to the PCM...?? They can break in the sheathing and cause issues....a continuity test will verify if it's ok.

Lord Knobrot


Hi sorry my thread didn’t come up, had no intention of spamming! Did look to remove them, the cht wiring looks fine is receiving voltage too, it’s weird that it’s pinned with absolutely no battery connected and no ignition but it doesn’t seem stuck, the engine will not turn over at all unless the fans are on max it won’t start though regardless, cheers for the suggestion.


Possibly a faulty gauge then.. or the clocks PCB not happy.??

Lord Knobrot
2008 2.4L RWD 170+PS 6-speed 350 LWB High Roof.

When I die, I want to go peacefully in my sleep like my Grandfather, not screaming like the passengers in his car..!
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Re: Super Weird Fault "Overheat"

Postby Cretosx » Mon Jan 24, 2022 4:15 am

knobby1 wrote:
Cretosx wrote:
knobby1 wrote:Have you checked the CHT wiring connector and loom all the way back to the PCM...?? They can break in the sheathing and cause issues....a continuity test will verify if it's ok.

Lord Knobrot


Hi sorry my thread didn’t come up, had no intention of spamming! Did look to remove them, the cht wiring looks fine is receiving voltage too, it’s weird that it’s pinned with absolutely no battery connected and no ignition but it doesn’t seem stuck, the engine will not turn over at all unless the fans are on max it won’t start though regardless, cheers for the suggestion.


Possibly a faulty gauge then.. or the clocks PCB not happy.??

Lord Knobrot


Could a faulty gauge stop it starting though? It’s really odd.
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Re: Super Weird Fault "Overheat"

Postby knobby1 » Mon Jan 24, 2022 6:21 am

Cretosx wrote:Could a faulty gauge stop it starting though? It’s really odd.


Just thinking out loud here and I'm probably talking out my ar$e...but.....If the PCM "thinks" the CHT is too high, it won't let the engine start. You've replaced the CHT sensor, so I'm guessing there may be a short somewhere in the wiring/gauge for this to be the case. If as you say, the gauge is stuck on high even with or without power to the clocks, I suspect there's possibly something wrong with the gauge. Once powered up, the gauge then tells the PCM the cyl head temp is too high....which = no start.


Lord Knobrot
2008 2.4L RWD 170+PS 6-speed 350 LWB High Roof.

When I die, I want to go peacefully in my sleep like my Grandfather, not screaming like the passengers in his car..!
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Re: Super Weird Fault "Overheat"

Postby Cretosx » Mon Jan 24, 2022 6:30 pm

knobby1 wrote:
Cretosx wrote:Could a faulty gauge stop it starting though? It’s really odd.


Just thinking out loud here and I'm probably talking out my ar$e...but.....If the PCM "thinks" the CHT is too high, it won't let the engine start. You've replaced the CHT sensor, so I'm guessing there may be a short somewhere in the wiring/gauge for this to be the case. If as you say, the gauge is stuck on high even with or without power to the clocks, I suspect there's possibly something wrong with the gauge. Once powered up, the gauge then tells the PCM the cyl head temp is too high....which = no start.


Lord Knobrot



So I think the fault lies with the PCM, the temp gauge isn’t stuck because I’ve taken it all out and it shoots straight up to 132C which is “fault to circuit” with the CHT I’ve checked all obvious wires, I’ve managed to start it with starter fluid but it will only turn over with the fans on, I don’t know if there is a fuse or relay that could cause this fault?

Thanks
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Re: Super Weird Fault "Overheat"

Postby Frag » Mon Jan 24, 2022 8:52 pm

I’ve had this fault with engine wiring loom rubbed through,check the area along front of timing cover where the loom should run in the plastic channel held on by 3 torx bolts.
There was a recall for the loom chafing,on the long bolt that holds the thermostat housing.

Fault I had,would cause van to cut out for a split second,usually before you had time to see the temp gauge ‘react’
Once I noticed that,fixing it was straight forward.
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Re: Super Weird Fault "Overheat"

Postby Cretosx » Mon Jan 24, 2022 9:47 pm

Frag wrote:I’ve had this fault with engine wiring loom rubbed through,check the area along front of timing cover where the loom should run in the plastic channel held on by 3 torx bolts.
There was a recall for the loom chafing,on the long bolt that holds the thermostat housing.

Fault I had,would cause van to cut out for a split second,usually before you had time to see the temp gauge ‘react’
Once I noticed that,fixing it was straight forward.


I did test the voltage going to the CHT sensor from that wire at it was 8V do you know what it’s supposed to be? I have checked around that but not in depth so I’ll definitely look tomorrow.

Thanks
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Re: Super Weird Fault "Overheat"

Postby eldertaco » Tue Jan 25, 2022 4:12 am

That sounds like much too high voltage, I would have expected something around 3.5v. This old post from wojciech might shed some light on it for you?

viewtopic.php?f=2&t=187190#p1602992
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Re: Super Weird Fault "Overheat"

Postby Cretosx » Tue Jan 25, 2022 1:03 pm

eldertaco wrote:That sounds like much too high voltage, I would have expected something around 3.5v. This old post from wojciech might shed some light on it for you?

viewtopic.php?f=2&t=187190#p1602992


What would cause something like this though?
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Re: Super Weird Fault "Overheat"

Postby Cretosx » Wed Jan 26, 2022 6:37 pm

Cretosx wrote:
eldertaco wrote:That sounds like much too high voltage, I would have expected something around 3.5v. This old post from wojciech might shed some light on it for you?

viewtopic.php?f=2&t=187190#p1602992


What would cause something like this though?


I’m starting to lose the will to live over this, I’ve even disconnected the PCM and the temp gauge shoots to H still, disconnected the cht sensor, removed the entire dash and gauge assembly and looks all in good working order, checked all the CHT wire cable and it looks absolutely fine please someone help, I’ve asked a few mechanics and no one locally seems to know what is wrong, otherwise I’m going to have to scrap my old girl
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Re: Super Weird Fault "Overheat"

Postby Frag » Thu Jan 27, 2022 3:12 pm

Have you checked the continuity of the wiring from the CHT to the PCM ?
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Re: Super Weird Fault "Overheat"

Postby Cretosx » Sat Jan 29, 2022 2:00 pm

Frag wrote:Have you checked the continuity of the wiring from the CHT to the PCM ?

Unfortunately I have and it all looks normal, is it possible the actual gauge cluster itself is at fault?
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Re: Super Weird Fault "Overheat"

Postby wojciech » Sat Jan 29, 2022 3:42 pm

In addition to the PCM reaction to the CHT sensor indications, indicating that the engine is overheated (regardless of whether the CHT sensor is actually working properly or is damaged), the system has implemented appropriate behaviors depending on the damage to the circuit - including the wiring harness.

- if the electric circuit of the CHT sensor is open, the system adopts maximum temperature value of 120 ° C, the PCM puts the motor in the overheating protection mode, the fans run at full speed, the injection dose is reduced and, if necessary, AC is turned off.

- in the event of a short circuit in the electric circuit of the CHT sensor, the system takes the value temperatures > 132 ° C. In this case, the engine either cuts out or cannot run it. This is probably your case:
Cretosx wrote:So I think the fault lies with the PCM, the temp gauge isn’t stuck because I’ve taken it all out and it shoots straight up to 132C which is “fault to circuit” with the CHT I’ve checked all obvious wires, I’ve managed to start it with starter fluid but it will only turn over with the fans on, I don’t know if there is a fuse or relay that could cause this fault?
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