steam
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Post by steam on Jan 31, 2023 8:43:39 GMT
Hi, I'm getting a coolant flow error and whilst investigating I came across a strange reading for "Sensor for engine block temperature, raw value". This is reading -48°C, which can't be right. The problem is I don't know where the sensor is located or what the part number is. Any suggestions?  |
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Post by dv52 (Australia) on Jan 31, 2023 21:06:53 GMT
steam : Hi. OK, I guess the first point to make is to explain the diagnostic conclusion that can be made from a temperature sensor that has a reading of -48°C. These transducers work by translating temperature into electrical resistance. The material that is used in most (but not all) of these sensors has what engineers call a "Negative Temperature Coefficient" (NTC) - which means that the sensor resistance decreases as the temperature increases. So, the circuits inside the Engine Control Unit (ECU - it's the module with CAN address hex01) that measure engine temperature interprets low sensor resistance with high engine temperature and vice-a-versa. And importantly, these circuits are designed with an upper and a lower temperature value, so that the maximum/minimum reading makes sense. With this explanation as a backdrop, a reading of -48°C is generally the designed lower threshold temperature that the ECU can read from these sensors. Because of the NTC nature of the sensor, this reading means that the inherent resistance of the temperature sensor is very high. From a diagnostic perspective, a reading of -48°C infers that the circuit resistance is "Open Circuit" - which means that either the sensor itself has failed, or there is a problem with either the sensor wire, or a sensor-wire connection to the ECU. Now, it really does depend on the engine type on the car - but in general there are 2 x temperature sensors like this: - Coolant temperature sender - G62- located on the cylinder head (normally @ the gearbox end)
- Radiator outlet coolant temperature sender - G83- located in the outlet coolant hose (normally)
Unfortunately, your screenshot is not complete, but it suggests that the engine in this car has both G62 & G83. But, I repeat, it really does depend on the engine type!!! You can confirm the engine type from the SCAN report - it's normally disclosed on the ECU detail. As an example, this is the layout for the 2 x temperature sensors on a CJXC engine (2.0 l, 4 V, turbocharger, chain drive, generation III) - it's from a previous reply to another thread:
Don
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steam
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Post by steam on Jan 31, 2023 22:13:37 GMT
Hi Don. Thanks for the info and very good guess with the engine  Sorry. I should have stated that. I haven't had a chance to look at it again, but what you state about the -48°C is what I suspected. Either that or a short. I guess the easiest way to check which one is faulty is to disconnect the easiest one to get to. Thanks again |
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steam
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Post by steam on Feb 6, 2023 21:04:52 GMT
 I'm getting a bit confused by this now. The coolant temperature at radiator output, specified value is giving -48, but the actual temperature is 17.4 (holding sensor in my hand). Where is this specified value coming from? I've checked both G62 and G83 and both appear to be working OK, but I still get the Sensor for engine block temperature, raw value -48. Is there another sensor which could be giving this? |
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Post by dv52 (Australia) on Feb 6, 2023 21:48:33 GMT
steam : I'm not sure how the "specified value" is determined - but my hunch is that it's a value that is calculated by an algorithm in the engine module and that it is based on the "actual" temperature readings from one, or more-likely multiple sensors. Again, my guess is that the formula in this "specified value" algorithm has upper and lower limits - and in this case, the lower limit is binding because one of the "actual" temperature values is -48°C
Anyway, if you have confirmed that G62 & G83 are working properly and if you are still getting a -48°C reading for the engine block temperature - then perhaps the latter part of my previous suggestion might be worth investigating? From a diagnostic perspective, a reading of -48°C infers that the circuit resistance is "Open Circuit" - which means that either the sensor itself has failed, or there is a problem with either the sensor wire, or a sensor-wire connection to the ECU. I only have wiring diagrams for RoW model mk7.5, but for an engine type CJXC, there are no intervening connectors on the wires for either of the 2 x temperature sensor. So, it's one-piece wire for each circuit!
I would be surprised if the connections at the ECU end are faulty - but it's still possible! More likely, the state of the connector plug at the sensor end might be worth carefully eyeballing and testing with a multi-meter (IMO, of course)
Don
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steam
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Post by steam on Feb 6, 2023 22:14:48 GMT
Hi Don. Thanks for the reply. I've checked through the wiring to the 2 sensors and all looks good. I'm beginning to thing that I maybe hit on something while I was testing and the -48 is somehow a calculated value from a historical reading. I've not had the car running for any length of time since I started looking into this. I've got the wiring diagrams for the CJXC and the only other sensor I can see is the oil temp one, which seems to be giving a sensible reading. It's a bit late in Scotland, so I'm leaving it for tonight. I think my plan is just to double check everything and if it all checks out OK to run the car for a while to see if the specified value changes. It's quite an interesting issue |
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Post by dv52 (Australia) on Feb 7, 2023 3:29:59 GMT
It's quite an interesting issue
Indeed it is!!!
But then, ALL diagnostic problems on the cars on this forum are "quite.....interesting"! This is the ONLY reason why I'm here - and of course because I'm a fervent believer in OBD11 (only kidding, I'm not - VCDS and VCP and OBD11 each have their individual advantages and peculiar deficiencies!!)!! Anyhow - just for my own curiosity - how did you ascertain that the temperature sensors (G62, in particular) were OK? And, as you will already know because you have the A3 8V wiring diagrams, stuff changed on CJXC engines for cars that rolled-off the assembly line after November 2015. When was this car built?
Don
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steam
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Post by steam on Feb 7, 2023 20:38:09 GMT
I measured continuity from the ECU to the sensors and that was OK. I did a very unscientific method of testing the sensors. I pulled them out and measured the impedance. I then warmed them up in my hand and measured them again. Both dropped from around 4.5k to about 2.5k.
Ive just had the car idling for about 30 minutes and everything seems quite stable. Unfortunately its about 4deg here at the moment, so couldn't get it very hot. Temp readouts seemed OK and the pump valve was open about 10%. The outlet at the radiator didn't change much and sat at roughly 10deg compared with engine temp of 93deg, but I did the touching it test and it was indead quite cold. The radiator seems to be doing it's job very well. Even with the fans off. The top hose to the radiator was nice and warm, so it seems like there was flow going through it.
The -48 deg was still there thoughout.
So, it seems like everything is working apart from the -48deg. I guess all I can do now is go for a prolonged drive and see if I can get it to fault again, then see whats happening.
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zaggy
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Post by zaggy on Jun 18, 2023 11:19:15 GMT
Hey, have you solved the issue with the -48°C, coolant temp at radiator output:specified? Mine showing the same aswell.
Would appreciate your reply!
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Post by dv52 (Australia) on Jun 18, 2023 22:10:51 GMT
zaggy: more information needed! Which engine (meaning like CJXC) is in this car and what was the build year? Don
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Post by rayc86 on Nov 25, 2023 16:09:39 GMT
Hey
I've stumbled in from a Google search and wondering if you managed to sort this?
I've a 1.2tsi cbzb and rad output temp is saying -48 aswell as fans not activating under temperature.
I've used a suitable wire to bridge the fan switch connector and pins 1-2 give me low and 1-3 give me high speed so I've assumed this means all the wiring is correct?
I've purchased a replacement meyle fan switch but again this reads -48c
Top rad hose gets warm then hot and return line from the top rad also gets very hot.
Bottom rad hose.gets warm but not at warm as top hose this gives me the surgestion that the rad is flowing?
Could the fan switch be getting fluid is it possible to block in a specific area? Limiting flow?
Totally lost with this coolant boils over and cabin has cold air but if heaters left off whilst driving then putting th on shortly blows hot then cools to cold withing a minute.
Any help really appreciated
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Post by brandonrs on Apr 28, 2024 20:46:47 GMT
Hey I've stumbled in from a Google search and wondering if you managed to sort this? I've a 1.2tsi cbzb and rad output temp is saying -48 aswell as fans not activating under temperature. I've used a suitable wire to bridge the fan switch connector and pins 1-2 give me low and 1-3 give me high speed so I've assumed this means all the wiring is correct? I've purchased a replacement meyle fan switch but again this reads -48c Top rad hose gets warm then hot and return line from the top rad also gets very hot. Bottom rad hose.gets warm but not at warm as top hose this gives me the surgestion that the rad is flowing? Could the fan switch be getting fluid is it possible to block in a specific area? Limiting flow? Totally lost with this coolant boils over and cabin has cold air but if heaters left off whilst driving then putting th on shortly blows hot then cools to cold withing a minute. Any help really appreciated Hi did you get anywhere with this? Having the exact same problem currently and really struggling to find the problem feel like I’ve tried everything. |
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desh
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Post by desh on May 8, 2024 9:58:32 GMT
Hey I've stumbled in from a Google search and wondering if you managed to sort this? I've a 1.2tsi cbzb and rad output temp is saying -48 aswell as fans not activating under temperature. I've used a suitable wire to bridge the fan switch connector and pins 1-2 give me low and 1-3 give me high speed so I've assumed this means all the wiring is correct? I've purchased a replacement meyle fan switch but again this reads -48c Top rad hose gets warm then hot and return line from the top rad also gets very hot. Bottom rad hose.gets warm but not at warm as top hose this gives me the surgestion that the rad is flowing? Could the fan switch be getting fluid is it possible to block in a specific area? Limiting flow? Totally lost with this coolant boils over and cabin has cold air but if heaters left off whilst driving then putting th on shortly blows hot then cools to cold withing a minute. Any help really appreciated Hi did you get anywhere with this? Having the exact same problem currently and really struggling to find the problem feel like I’ve tried everything. Hi, me also I have the exact same situation. If you managed to resolve the problem any help would be much appreciated. Thanks |
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Sorry. I should have stated that.