Dear Lord - Subaru Electrical Experts Please Help :'(

[THUNDA]

Heya Team

 

Been chasing an electrical issue in my BC5 thats driving my crazy

 

I have 2 issues which I think are related to each other

 

Issue 1 - I Keep getting a code 43 (which from my research is TPS) - Have replaced the TPS 3 Times, with TPS's that bench test fine, resistance testing found the wire that the sensor uses to send info the the ecu had 1.6ohm resistance compared to the power feed from the Ecu to the tps which was 0.006ohms so i replaced it, every time after resetting the codes it throws code 43 after a few minutes of driving, this is the old TPS with the built in idle switch, idle switch tests fine and does not throw idle switch code 42

 

Issue 2 - I have continuity between my positive and negative battery leads  (wtf?) low resistance 

I tested the same test on my ute and there is no continuity between my battery leads

 

Was thinking maybe the alternator could be damaged somehow, as I havnt seen it put out more than 13.4V but i do leave my battery on a trickle charger so I guess the alternator doesnt have much to do in terms of needing the make power 

 

Any suggestions would be great

I have an awesome multimeter now so just need to be pointed in the right direction ive spent hours over the past few weekends under the hood / fuse box area 

 

(Note: I have found fault code lists that say 2 different codes for TPS, one code says TPS is 31 Throttle Position Sensor or Circuit  and 43 Throttle Switch and another says 43 TPS and 31 nothing

 

 

[Gripless]

Ok…

1) what sensor do you have for the TPS and idle stepper do you have the pin out diagram so you can test them correctly.

 

2) are you following the TPS install procedure if the sensors are secondhand? Depending on the model they can rotate too far or past full or zero. That can upset the ecu it the tps reads closed but the switch reads open. When you test drive are you only using low throttle? Once fitted test the resistance stays nice and linear from closed to open, and then retest the closed to open the closed switch is only when closed.

 

3) have you cleaned the connector and if needed put small cable tie around plug and sensor. You need to check the ecu end as well. Plus check the ecu end run an extra wire to the sensor plug and shake the wires incase there’s a break that gets exposed. 

4) for the battery are you sure the terminal isn’t touching something while it’s pushed back like that?

[THUNDA]

13 hours ago, Gripless said:

Ok…

1) what sensor do you have for the TPS and idle stepper do you have the pin out diagram so you can test them correctly.

 

2) are you following the TPS install procedure if the sensors are secondhand? Depending on the model they can rotate too far or past full or zero. That can upset the ecu it the tps reads closed but the switch reads open. When you test drive are you only using low throttle? Once fitted test the resistance stays nice and linear from closed to open, and then retest the closed to open the closed switch is only when closed.

 

3) have you cleaned the connector and if needed put small cable tie around plug and sensor. You need to check the ecu end as well. Plus check the ecu end run an extra wire to the sensor plug and shake the wires incase there’s a break that gets exposed. 

4) for the battery are you sure the terminal isn’t touching something while it’s pushed back like that?

 

1 - My TPS is the 4Plug A22-000R25

Ive tested them using the resistance method, i know which wires are IDLE SW / GND / 5+ from ECU / SIGNAL to ECU looked for a smooth resistance signal while rotating the actuator on bench test all 3 TPS didnt have any jumping or skipping in resistance - but yes this is definitely a factor - also to note after clearing the code it usually comes back when on low throttle / coasting 

Note: The resistance in all 3 TPS sensors Start around 2.4hms at Closed Throttle, then they all go up to around 3.0ohms, then down to around 1.3ohms at wide open throttle

 

2 - TPS installation procedure - I feel I have tried every procedure - but stuck to the book, even made live adjustments with the car running (this is how i got rid of the idle switch fault code) 

Voltages

IDLE SW -  40MV Closed 4.87V Open

+VE from ECU - 5.18V

TPS Send to ECU wire - 4.75V Closed 0.89V Open

 

3 - Yes connector is clean but does feel a little loose, ill try tighten it up

I tested all the wires from the TPS that lead to the ECU, found a great ECU pinout which made it easy as

Ran a wire from TPS connector outside the car to near the ecu so i could test resistance, and the SIGNAL wire had a resistance of 1.6Ohm so i replaced the wire with new, now 0.006 Ohm, all other TPS wires at ecu tested 0.006-0.008ohms 

 

4 - I carried out the same test this morning (cold) and got completely different results compared to when i checked last night while car was still hot - i put a rag under the terminal and got 20 Killa Ohms between positive and negative terminals - so thats very high resistance but still some potential there which is a little weird, comparing it to my ute there is no potential between positive and negative  - i gave the earth terminal a clean + sand and battery post a clean + sand and now have 0.0001ohms so i have lowered the earths resistance and it is uniform when tested around the engine 

[THUNDA]

Small update - after trying for an hour to track down the resistance reading

 

I can only get 2 circuits to change the resistance reading (resistance between +ve and -ve terminals with battery disconnected is 22kOhm) is when i unplug the alternator (at the 5plug) as soon as i unplug the alternator it changes resistance to 33kOhm, and the second one is the big wire fuse in the engine bay fuse box, when i unplug that it breaks the circuit - which is great but doesnt help me narrow it down

 

I tested alternator by running car with all lights and AC on and it produced 14.4Volts easy 

 

I really dont want to take it to a workshop, im not sure whats happening to the industry but every time i take it to a workshop it comes back with damage, even the guys who did my clutch kit threaded one of the gearbox bolts -_ -

[Gripless]

1) What’s the battery resistance when you unplug the ecu?

 

2) what’s the idle stepper motor resistance like? If it’s off throttle coast th ecu should be adjusting the stepper motor to keep rpm on target. You should get matching resistance between the pair of pins that are coils.

 

[THUNDA]

9 minutes ago, Gripless said:

1) What’s the battery resistance when you unplug the ecu?

 

2) what’s the idle stepper motor resistance like? If it’s off throttle coast th ecu should be adjusting the stepper motor to keep rpm on target. You should get matching resistance between the pair of pins that are coils.

 

Will check after work tomorrow

Idle stepper motor - do you mean the IACV ? ive been hesitant to even touch this incase i cause another electrical fault haha, but yeah ill check it tomorrow arvo 

[Gripless]

Do you get high idle when cold start or when moving power steering at idle?

if that works then maybe it isn’t bad.

 

sounds like a bitch to deal with too.

https://forums.nasioc.com/forums/showthread.php?t=781242

 

i haven’t done the Subaru one but mid nineties mitsi had those same screws and I had to drill them as the screw heads failed.

Edited May 25 by Gripless

[THUNDA]

17 hours ago, Gripless said:

Do you get high idle when cold start or when moving power steering at idle?

if that works then maybe it isn’t bad.

 

sounds like a bitch to deal with too.

https://forums.nasioc.com/forums/showthread.php?t=781242

 

i haven’t done the Subaru one but mid nineties mitsi had those same screws and I had to drill them as the screw heads failed.

 

Yup high idle when cord start / turning on lights and ac etc

IACV resistance between each coil and earth 10ohms, coil to coil 16ohms

 

unplugging ecu doesnt change the resistance leak to earth

 

ill do some more fuse pulling on the weekend, could even be something as simple as an oily sensor plug... this car doesnt have any oil leaks but hell im willing to try anything haha 

[Gripless]

How old is the battery?

then there’s always the rectifier on the alternator, they can go bad.

either of those only show up under load to start with.

[boon]

Something is f***ed here, if you put a car battery across a 1 ohm load you get a good spark and a lot of heat very quickly. Unless everything involved is rather large.

 

Suspect something is kooked with your alternator.

[THUNDA]

3 hours ago, boon said:

Something is f***ed here, if you put a car battery across a 1 ohm load you get a good spark and a lot of heat very quickly. Unless everything involved is rather large.

 

Suspect something is kooked with your alternator.

 

Battery tests fine, no resistance between battery posts when its disconnected from the car

i only get resistance of 15ohms when i disconnect the +ve lead and test between +ve lead (not battery post) and negative  lead but yeah i realise thats f***ed haha, thats why as soon as i tested it i was like arrrrrrrr that not good 

 

Yeah i might just order a new alternator to rule it out - heres hoping i can find one haha 

[Gripless]

Likely the alternator has a replaceable rectifier unit inside.

some can even be disassembled and individual diodes replaced.

 

 

[boon]

f*** it just get one from Pickapart, they're like $40.