This is very interesting. I take it your ECU is a Bosch, same as mine?
Do you have any codes present with this 3.3v ? Any symptoms at all, like weird temp gauge readings ?
Moderator: RichardW
MikeT wrote: ↑14 Sep 2017, 13:53
I believe max tested the sensor and even replaced it which is the fault code you see but as the circuit (without sensor) was also tested as no good, that's where we're at.
Yeah, I get that but it's so frustrating I sought humour being flippant. I should know by now it never translates well, should have kept it to myself.ekjdm14 wrote: ↑14 Sep 2017, 10:24
Not quite, as I see it the ref voltage should always remain at 5v and the ECU takes it's readings through resistive sensors that pass a percentage of said voltage to ground through the ECU's measuring medium. The only time the ref voltage itself ought to vary from 5v is if there's either a short in said circuit that loads the driver beyond it's capability to maintain this steady voltage (likely in the wiring prior to the sensor input IMO) or if there's a faulty component providing the voltage.
Before Darren's input (excuse the pun ), I could find no other examples of a 3.3v signal input, in fact scannerdanner was the only place that came close, with reference voltages at either a lower 1.7v or 0v. Maybe my search methodolgy is lacking but that's all I found.ekjdm14 wrote: ↑14 Sep 2017, 10:24
In this case I'm taking the fact that 2 separate ECUs have faults where a reference voltage has dropped to the same exact level within 0.1v to mean it's more likely than before that there's a common failure mode within the ECU's driver circuitry that causes this drop. That's not to say it isn't just a wiring fault, just that in my (inexpert!) opinion, the likelihood of faulty ECUs in both cases has gone up by a large percentage.
Also interestingly, many of the case studies scannerdanner uses are engine swaps (as with max's situation) with faults such as frayed rubbing or pulled looms, rotten earths and misconnected wires, faulty sensors as well as one case of reverse polarity when using a bluepoint professional charger - on booster mode - which made the battery explode! That DID fry the ECU.
Obviously, that's a way too small a sample to draw any meaninful conclusions from but scannerdanner has stated that symptoms of a failed 5v supply often equates to no comms with the diagnostic scanner too. i haven't found anything to confirm this though.
I think I made it clear way back when the ECU 5v pin measured 3.3v, I accept the ECU may well be at fault but since then we've got no closer to a definitive diagnosis leaving max facing even more expense he can ill-afford.
MikeT wrote: ↑14 Sep 2017, 13:53Yeah, I get that but it's so frustrating I sought humour being flippant. I should know by now it never translates well, should have kept it to myself.
no worries, I "got" that the sceptical kid was in humour just felt I needed to clarify why I was going further towards suspecting the ECU
many of the case studies scannerdanner uses are engine swaps (as with max's situation) with faults such as frayed rubbing or pulled looms, rotten earths and misconnected wires, faulty sensors as well as one case of reverse polarity when using a bluepoint professional charger - on booster mode - which made
ekjdm14 wrote: ↑14 Sep 2017, 15:07
Now, this is something I didn't know... I may be getting confused with other threads here but I'd swear that I read this car was running and just stopped? Now, if this is indeed an engine swap then I'd have to lean back toward a pinched/pulled wire or perhaps a couple of close components having their connectors swapped round. (on that last point, I know there's no other fault codes but does absolutely everything else on the car work perfectly as it ought to, headlamps/fogs/wipers/blowers and the like? I appreciate the AC is impossible to test with a non runner but just to rule out an accidental plug switching between components).
Definitely I'd be looking at the wiring like a hawk if its an engine swap though.
ekjdm14 wrote: ↑14 Sep 2017, 19:53 Ah, that's a strange one yes So rather than all being "rosy" from the get-go it's always had ECT issues (just since the swap? or did it have a problem here prior to the swap do we know? That'd make a difference to where the cause likely is).
If it's just been since the swap then I'd look to wiring either pinched or chafing (probably the latter given the car's "downhill spiral" of late) but again if the coolant gauge was iffy even before the engine swap then it'd point my eye toward the ECU again.
Actually, it may be relevant maybe not, but what was the reason for the original engine swap? possible clues there too?
MikeT wrote: ↑14 Sep 2017, 20:03ekjdm14 wrote: ↑14 Sep 2017, 19:53 Ah, that's a strange one yes So rather than all being "rosy" from the get-go it's always had ECT issues (just since the swap? or did it have a problem here prior to the swap do we know? That'd make a difference to where the cause likely is).
If it's just been since the swap then I'd look to wiring either pinched or chafing (probably the latter given the car's "downhill spiral" of late) but again if the coolant gauge was iffy even before the engine swap then it'd point my eye toward the ECU again.
Actually, it may be relevant maybe not, but what was the reason for the original engine swap? possible clues there too?
I think the coolant reading fault was after the engine swap but best let max answer those historical questions before I cause more confusion.
ekjdm14 wrote: ↑14 Sep 2017, 20:10MikeT wrote: ↑14 Sep 2017, 20:03ekjdm14 wrote: ↑14 Sep 2017, 19:53 Ah, that's a strange one yes So rather than all being "rosy" from the get-go it's always had ECT issues (just since the swap? or did it have a problem here prior to the swap do we know? That'd make a difference to where the cause likely is).
If it's just been since the swap then I'd look to wiring either pinched or chafing (probably the latter given the car's "downhill spiral" of late) but again if the coolant gauge was iffy even before the engine swap then it'd point my eye toward the ECU again.
Actually, it may be relevant maybe not, but what was the reason for the original engine swap? possible clues there too?
I think the coolant reading fault was after the engine swap but best let max answer those historical questions before I cause more confusion.
Yes, I'll leave it for Max to come back on these bits of info as & when he has the time/inclination to think about sorting the car again. I can well understand if he needs to take a break from the thing now, knowing how frustrating it can be to spend good money and still be left with an unusable car. Just hoping we can get it sorted as I'm sure we both would like to see a positive outcome as well as Max.
Not the same symptoms so wonder if this^^^ is effect (of coolant ingress), rather than cause?Diagnostic information
Engine temperature (too) high and cooling fan runs continuously
Fault on 5 volt circuit
I guess the problem here is determining what a normal current draw should read and then having the test equipment to detect it?Doing this reference voltage test requires measuring for both proper voltage level and current draw on the same wire at the same time as shown in Figure 1. We need both current and voltage to be measured to first determine whether the lack of 5V reference is due to the PCM not being able to output the proper voltage because of an internal defect. In this scenario, the voltage will be low and very little current will be flowing in that reference wire. On the other hand, if the proper voltage output from the PCM is being pulled low due to a shorted sensor or harness defect, the voltage still will be low, but too much current will be flowing in the wire. The current flow level in the wire is the key in determining which of these two defects is the true cause of the problem.
MikeT wrote: ↑15 Sep 2017, 14:16 Here's a claimed definitive diagnostic test I've not seen mentioned before.
http://www.searchautoparts.com/motorage ... akdown-pcmI guess the problem here is determining what a normal current draw should read and then having the test equipment to detect it?Doing this reference voltage test requires measuring for both proper voltage level and current draw on the same wire at the same time as shown in Figure 1. We need both current and voltage to be measured to first determine whether the lack of 5V reference is due to the PCM not being able to output the proper voltage because of an internal defect. In this scenario, the voltage will be low and very little current will be flowing in that reference wire. On the other hand, if the proper voltage output from the PCM is being pulled low due to a shorted sensor or harness defect, the voltage still will be low, but too much current will be flowing in the wire. The current flow level in the wire is the key in determining which of these two defects is the true cause of the problem.