[Jackvine76]

Any help appreciated, as title says hard to start when cold and the glow plug light stays on for a long time.

So far Ive replaced.

All glow-plugs, all were open circuit, probably burnt out
Fuel filter
Coolant temp sensor
Ive put Vag-Com on and get the P1256 coolant temp sensor open or short.
Every time I reset it, it will instantly come back, I've checked in measuring block and get temperature readings that seem fine, even when the sensor is unplugged!

 

[Or_GazM]

Wiring loom from one side of the engine to the other (at the back)
Loads of posts about broken wires in it.....
ECU and Instruments have to communicate with each other and the sensors through that loom.
Only happens on RHD vans.

 

[hobbyhorse]

It's nothing to do with the glow plugs, they are not required this time of year (unless you're in the Arctic circle).

Classic symptoms of pump timing retarded - have you checked the timing ?

HH

 

[Jackvine76]

Pump timing checked on Vagcom and seems within spec, Ive also checked through loom and seems fine.
Im leaning towards the ECU as I can not reset the coolant temp sensor error, ive also checked at the sensor and there is a voltage from the ECU

 

[hobbyhorse]

Pump timing checked on Vagcom and seems within spec

What figure do you see on the timing graph ?
(engine above 80c)

HH

 

[shankalanks]

Hullo - I saw that you replaced the G62 coolant sensor, as recommended on the Ross Tech site and others, for P1256.
Can I ask which part-no. you went for, colour and no. of pins?
I find the info about this quite confusing and contradictory even though apparently your symptoms point to G62 failure.
My own sensor is shown here - 1998 2.5tdi ACV. I assume yours is the ACV 102bhp engine too? The 7Zap s-shot is for year 1998.
I’m asking as I don’t know if you tested your old sensor or whether you’re as confused as me about pins/colour/make/impact of these things.
I don’t know the part number of mine as it’s not visible and I’m not removing it just to find out.

 

[Jackvine76]

Hi Mine is the AJT engine 88bhp, and has the 2pin blue coolant sensor, ive not tested the original sensor yet, will test it tonight and see what it reads.

 

[hobbyhorse]

Any help appreciated, as title says hard to start when cold

This is peculiar.

A faulty temp sensor (P1256 ) usually gives you the reverse symptoms of this i.e. starts fine when cold but difficult when hot.

There are actually 2 temperature sensors on the 2.5 TDI:

The 4 pin sensor gives a signal to the instrument cluster & the aux pump, the 2 pin sensor supplies a signal to the ECU.

Have you changed the correct one ?

HH

 

[shankalanks]

This is peculiar.

So in this shot you're saying Part no. 7 is the G62 sensor and not part 8?

 

[Jackvine76]

This is peculiar.

A faulty temp sensor (P1256 ) usually gives you the reverse symptoms of this i.e. starts fine when cold but difficult when hot.

There are actually 2 temperature sensors on the 2.5 TDI:

The 4 pin sensor gives a signal to the instrument cluster & the aux pump, the 2 pin sensor supplies a signal to the ECU.

Have you changed the correct one ?

HH

2Pin Blue is what I have changed so far

 

[Jackvine76]

Part 7 is the item Ive replaced

 

[hobbyhorse]

Hi Shanka,

That pic (7zap ?) doesn't look correct - many don't & have had me scratching my head on more than a few occasions.

Here's the usual config:

+


ECU signal top, 4 pin sensor for clocks & aux on the side.

HH

 

[hobbyhorse]

Shanka, on your engine I see D5252T on the block which would suggest a phase 1 V70 rather than an T4 ACV ?

HH

 

[shankalanks]

Shanka, is yours from a Volvo ?

No H, no way. This is exactly why I’m confused about this. Here’s a fresh shot from above perspective:

I’ve seen in other forums that it’s the sensor only seen from below - but I’m so confused about this, so I can see why some just change all of the sensors here!

 

[shankalanks]

Part 7 is the item Ive replace

Hi - I’m not trying to hijack your thread. It’s just a useful opportunity to try and resolve this aspect.

 

[hobbyhorse]

No H, no way. This is exactly why I’m confused about this.

Just had a look at one here & indeed it too is marked as a D5252T ! you learn something everyday - never spotted that before.

I can only assume that there are differences in the water manifolds depending on the van year.

The 4 pin sensor contains part refs. G2 & G62 within the same body.

HH

 

[shankalanks]

The 4 pin sensor contains part refs. G2 & G62 within the same body.

So is that no7 or no8 or is me being thick?

BTW: There’s a series of You-Choob videos by ‘diesel bricks’ who does the timing & more on a Volvo D5252T which might be useful for anyone about to do the same on an ACV.

 

[hobbyhorse]

So is that no7 or no8 or is me being thick?

It's not you - the circuit schematic & 7zap do not correspond; probably differences across the production years.

Any doubt change 'em both.

HH

 

[hobbyhorse]

OP,

Check the fuel sender unit is not cracked, this allows the fuel to drain back to the tank overnight & causes poor cold start

HH

 

[Jackvine76]

Has anyone got a circuit diagram that’s shows the ECU sensor, and where it goes into ECU ?