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Old 02-12-2014, 07:34 AM
raw raw is offline
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Default Glow Plug Relay

Anyone able to explain the reasons behind my GPR having failed in such a way that it is on any time when it is connected to the ignition live and the ground (i.e. whenever the blue ign live and the black ground are connected).

i have checked the signals from all the wires to it and am getting voltages that make sense from ign live, start live, warning lamp, and earth, but i don't know what the voltage from the temperature sensor should be. with the engine hot at the moment the temperature sensor signal is 0V, thought it was 11.2V when it was cold but i'm not sure.

i have checked all the internals of the relay unit, cleaned the relay contacts which are free moving and work fine (it goes on and off fine when the power is connected/disconnected), and all the solder joints on the circuit board have been reflowed despite seeming to be fine.

as far as i can tell now i'm down to the possibilities being the PCB or the temperature signal from the cylinder head temperature. some photos below of the relay unit incase anyone might be able to see anything amiss, though i somehow doubt it.







cleaned up the relay contacts with wet and dry after taking that first photo and they're now nice and shiny, but it's changed nothing at all :|

Richard
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Old 02-12-2014, 07:58 AM
jpliddy jpliddy is offline
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Default 940 tdi auto 1995

hi raw i cant help with this one i have never had this relay of the car yet .
but red the relay fuse needs cleaning or replacing from time to time as our cars become ancient .
pretty sure some one here can help .
try volvo owners club forum thats where i have seen some comments
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Old 02-12-2014, 09:27 AM
raw raw is offline
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I shall repost the post above in the 700/900 section and in the diesel section but I find there doesn't seem to be as much real knowledge about these engines on there, lots of people 'know' they're rubbish but most don't actually know as much as some of the genii on here.

Richard
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Old 02-12-2014, 01:46 PM
745 TurboGreasel 745 TurboGreasel is offline
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are you sure it's not a wiring harness problem?
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Old 02-12-2014, 02:03 PM
ngoma ngoma is offline
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Quote:
Originally Posted by raw View Post
...with the engine hot at the moment the temperature sensor signal is 0V, thought it was 11.2V when it was cold but i'm not sure.
Temp sensor is ground, should read higher resistance when cold, resistance diminishing (towards 0 ohm) with rising temp. That is why we can trick the GPs into operating at every startup regardless of temp by disconnecting the wire from the temp sensor. Helpful for getting a tired low-compression engine started when warm. The GP controller "sees" the disconnected sensor wire as extreme cold temp and energizes the GPs. Which is what your symptom looks like.

Try measuring resistance (might be labeled as ohms Ω on your meter) at the temp sensor instead of current.

Another troubleshooting trick: If your temp gauge works, run a temporary jumper from the temp gauge temp sensor (the one near GP #1) to the GP relay temp (brown) wire. If this makes the GP relay work correctly, then the GP temp sensor at the back of the head is faulty.
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Old 02-12-2014, 02:17 PM
raw raw is offline
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my fault is that the glow plugs just run constantly, i cannot get the relay to reenergise without disconnecting it from either ground or the blue ign live.

measured voltage (expect you didnt mean current as i can't think how you could test the current to it without a bit of a faf) since it's easier than resistance given that i was testing the other signals at the relay for their voltage in different states anyway. regardless, my results seem to agree with the resistance you're suggesting i should have (high voltage when engine is cold and low when hot) so the issue doesn't seem to be there.

i know my wiring harness isn't great near the GPR particularly, the connector on the bottom of the relay is actually particularly bad and i've had to resolder all the connections into it, and bodge a replacement for one of the terminals that I simply couldn't resolver to anymore, but I'm sure it's all working. this issue is confusing and also quite annoying, especially seeing as working GPRs don't seem to be easily available to just whack one on to try!

the more i think about it i think the issue is probably a component failure on the PCB of the Glow Plug Relay, so i think i'll have a look into the circuit on the PCB to work out how it works, maybe one of the ICs that are on it is a proprietary timing chip in which case i'll try that first. whatever it is i'm sure i can refurbish the entire circuit board for less than the cost of a new Relay!

Richard
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Old 02-12-2014, 04:12 PM
745 TurboGreasel 745 TurboGreasel is offline
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Every bit of the harness is massively suspect...see if your relay works normally with all substitute wires.
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Old 02-12-2014, 11:51 PM
raw raw is offline
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Is that a well known thing or just looking at the bits of mine that are in pictures? I may try that, got to get the injection pump belt back on the v70 first though :/

Richard
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Old 02-13-2014, 01:32 PM
745 TurboGreasel 745 TurboGreasel is offline
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On all the US cars, the insulation inside the wire harness eats itself, and wires then can cross at random. Your may be new enough to be imune.
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Old 02-13-2014, 11:40 PM
raw raw is offline
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oh! i'd never heard of that issue! well half my loom is '89 and the engine bits are '95 so i don't know whether it will be ok! the thing is that the wires seem to be behaving as they should at the GPR end according to my multimeter :S

i'll have another look next time i'm home

Richard
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