306 HDi - No throttle response and stuck on 1300 rpm... Have I cooked my ECU?

[cecil]

Hi all,

I've recently been trouble shooting an issue with my 2000 306 hdi 90. The problem has been a slight but very noticeable hesitation/miss on acceleration through about 1700-2100rpm. It's especially bad at 2000rpm.

I've been looking into a few things - most notably the EGR, the TPS and the MAF.

Today things got a whole lot worse.. I was trying to test the MAF by back probing the plug and reading the voltage output of the sense wire when I accidentally shorted something. The engine was running at the time and it immediately jumped from idle to 1300rpm and stayed there. I turned the ignition off and re started the engine and it went straight back to 1300rpm. I tried to rev it and the throttle did absolutely nothing. It's not reading inputs from the TPS! I plugged the MAF back in and the rpm dropped slightly but only by about 50rpm.

I plugged my OBD reader in and got the following codes:
P0560 - System Voltage
P0190 - Fuel rail pressure sensor circuit bank 1
P0220 - Throttle/Pedal position sensor switch 'B' circuit
P0120 -Throttle/Pedal position sensor switch 'A' circuit
I reset the codes and switched off and on again. Only P0220 and P0120 returned.

I had a look at the live data from the reader and this is what I saw (note the MAF was unplugged at this point)

Interesting to note the intake air temp was reading 215deg no matter if the MAF was connected or not. Also with the MAF connected the airflow was something crazy like 300gp/s.

I also noticed that the interior clock along with the (after market) stereo had reset themselves like they do if you disconnect the battery.

I checked every fuse on the car (that I know of - are there any other than the engine bay box and the drivers footwell box?) and everything looked fine.

Does anyone have any ideas? Have I cooked my ECU??

Any help is much appreciated.

[GiveMeABreak]

It is a distinct possibility that you may have. The MAF wiring of course goes to the engine ECU so may upset that. What is your VIN and I’ll look into those faults.

[cecil]

Thanks Marc. A bloke on another forum suggested the same tactic he used when presented with the same symptoms which was to open up the ECU and have a look for any burnt tracks/components. I did that and can't see anything that looks like its fried.

VIN is VF3**************[VIN obfuscated, can be read by forum staff].

Cheers for the assistance!

[GiveMeABreak]

Unfortunately as this is an earlier model, I don't have any of those codes coming up for this engine - but they may simply be because it was an early year before this was made available in any great detail.

The generic PSA data says:
P0560: Battery voltage fault
P0190: Pressure sensor on the fuel injection rail: Value incoherence on starting or when stopped
P0220: Accelerator pedal sensor: Incoherence between the accelerator pedal tracks involving a release problem for the 'Easy move' system
P0120: EGR electric butterfly position fault: Drift in low limit adaptation

I think you may have the last code wrong as this doesn't correspond to what has been reported.... All the accelerator sensor data is in the P022* range.

I doubt you would find anything physically 'scarred' on the board, but that isn't to say it hasn't affected any of the chips which are very prone to voltage spikes. So very hard to diagnose this one. The throttle position sensor is still available from PSA (item 12). It is listed as part 1920X1 but also says '+ UNIT 1608878580 (1)' .

Some of those faults could be related to a specific issue and may well self-clear after several starts of the car. The remaining ones still relate to the TPS so maybe the tracks have worn out?

[MikeT]

Check the 5V reference signal(s) from the ECU. Their driver circuitry seem to be the weakest link of an ECU from what I've gathered.

[cecil]

I think you may have the last code wrong as this doesn't correspond to what has been reported.... All the accelerator sensor data is in the P022* range.

Thanks for looking into things for me mate. I'm definitely getting the P0120 though, and it seems to be related to the TPS "A" Circuit from what i'm seeing on google.

Check the 5V reference signal(s) from the ECU. Their driver circuitry seem to be the weakest link of an ECU from what I've gathered.

I've just taken readings from all pins in the TPS and MAF plugs with both the ignition on engine off, and then the engine running. From what I can see there's definitely something odd happening down the line in the TPS wiring. All these reading were direct from the loom side of the plugs whilst they were disconnected.

TPS Engine off - Engine on
Yellow 9.67v - 10.94v
Green 10.63v - 4.95v
Red 5.01v - 5.01v
White 9.67v - 10.93v

MAF Engine off - Engine on
1 Green 5.00v - 5.00v
2 Pink 12.07v - 14.03v
3 Red 4.95v - 4.95v
4 Blank (no terminal in use)
5 Yellow 0.01v - 0.00v
6 White 4.95v - 4.95v

Something I found interesting (maybe because I don't know what i'm really looking at) is that the Red and White wires off the MAF which are meant to be earth wires are reading 4.95v and have no continuity to any earth points I tried. The green wire off the TPS is also reading 4.95v when the engine is running - is this also the earth for the TPS? I understand there's a 5v reference circuit on most sensors but that looks like its the Green off the MAF and the Red off the TPS. Why would the others be reading 4.95v?
Does anyone have a wiring diagram they can share?

I've been doing some further research and discovered (i think) the MAF, TPS and Fuel rail pressure sensor all share a common earth which is prone to high resistance. This could be why i'm getting code p0190. Peugeot apparently approved a mod to cut the earth wires from the MAF plug and re-route them to a new earth. There's some chat about it here https://www.306oc.co.uk/forum/showthread.php?pid=560212

Unfortunately I live in a place with no pug specialists, and very few euro cars so i'm kinda out on my own. Any more help would be much appreciated!

Cheers

[GiveMeABreak]

I'll have a look at the wiring for this shortly - but I suspect the code reader TBH - it's not the first time I've seen these providing wrong information and that fault code is definitely wrong from the data I have. I look at the wiring for you in the interim and post back here shortly.

[GiveMeABreak]

The wiring diagram indicates:

TPS 1377: White = Accelerator pedal 1 position info 1378: Yellow = Accelerator pedal 2 position info 1391: Red = MIL-REQUEST signal 1392: Green = EOBD warning info	MAF 1408: Green = volts turbocharging solenoid valve / supply CC17: Pink = Engine Fusebox F5 Relay 5 1410: Red = turbocharging solenoid valve earth 2 1447: Yellow = turbo "bypass" butterfly solenoid valve 2 control 1448: White = compressor 2 air temperature signal

[cecil]

You're right, it could well be the code reader - it's just a cheap one off ebay!

Cheers for providing the diagrams. Excuse my lack of knowledge though - i'm a bit of a noob when it comes to auto electronics. What sort of voltages should I be expecting from each wire for both the TPS and the MAF plugs when referenced to battery negative?

[xantia_v6]

I don't have any documentation specific to your car, but each sensor should have a reference voltage (usually 5V) on one pin ground on another, and the others will have a voltage proportional to the parameters being measured. As mentioned above, loss of the 5V reference signal will upset lots of things.

[cecil]

I think the 5v references are okay. Solid 5v from the green and red off the MAF and TPS respectively.

I made an interesting discovery this morning. I went through with the MAF ground wires mod talked about earlier and cut them at the plug then extended them and re-routed to a solid ground under the battery. This didn’t change anything unfortunately, but Things got interesting when I tried piggybacking the green ground wire off the TPS to the same solid ground point. Suddenly I had throttle response once more! However the idle still sits in the 1200-1300 range.

I started to look for shorts in the ground wires and I couldn’t find anything. I checked for continuity between the TPS ground and every other pin on the ECU and found nothing.

Does this lead to the conclusion that I need a replacement ECU?
Has anyone had experience with the IMMO disabled ECUs from hdi-tuning?
Worth getting the remapped version for the extra few quid?

[Simple76]

Try disconnecting battery for 10mins might reset itself.

[picassodad]

I too have a 306 that from time to time increases engine idle revs, and, from time to time will reduce engine power when going around a right hand bend at speedo, but only very very occasionally.

The central locking has a mind of its won when it rains !

I have for some time suspected the loss of power and the higher than normal idle speedo to a make and break contact in the engine bay loom, below the ecu where it bends forward and experiences the engine movement most.

I have yet to "dive in" on this problem as she runs great with good fuel economy, the central locking being more important at the moment.

Try and get pp2000 or a delphi diagnostics, even the chinky copies are good. Sorry I cannot hep more, and, are all the earths good including the main earth to the gearbox. I have fitted extra earths to the engine as a precaution. Bad earths will play havock. I have also earthed the ecu metal backing.

[picassodad]

does your diagnostics show a view of the throttle operation as 2 bars ??

[cecil]

So this is where i'm currently at. In a last ditch effort, after re-routing the MAF earths and being very suspicious of the TPS earth, I cut and re-routed it to the same chassis earth as the new MAF ones. Viola! The car runs pretty much fine again!

I'm pretty sure something is fried within the ECU earth for the TPS and MAF (which is apparently shared) and so by bypassing the ECU and going direct to the chassis i've completed the circuit again.

My only issue now is that the ECU isn't getting MAF data. It is getting intake air temp though... so i'm not sure what's happening there.
I've finally ordered a Haynes manual so I can get a look at some electrical diagrams.

I'll dive into it again when the manual arrives.

Cheers for all the help!