Help us help you. By posting the year, make, model and engine near the beginning of your help request, followed by the symptoms (no start, high idle, misfire etc.) Along with any prevalent Diagnostic Trouble Codes, aka DTCs, other forum members will be able to help you get to a solution more quickly and easily!
Hey guys i have a few questions of some circuits that i am unfamiliar with..
1. 2006 vw polo 9n 1.6i
* cam sensor circuit
Its a hall effect 3 wire sensor.. from my knowledge on it, it has a 5v ref, a ground, and signal. How does the signal wire have battery voltage on it? How does a 5v sensor output more than 5v? Confused! I dont have a scope so i can't give a waveform, and the battery was low reading 10v only.. the sensor works, it's just something i dont understand.
* this car will not pulse the injectors or give it a constant 12v if the fuel pump doesn't work. Clever engineering?
Got this 1 fixed, it was faulty fuel pump wiring..
2. 2013 Audi A4 1.8tfsi 8k chassis
* this car has 12 fault codes all concerning 5v sensors. I was thinking along the lines of a shorted out sensor. I decided to test the 5v ref on 2 of the map sensors:
Sensor 1: has 5 volts when unplugged, plugged on and back probed it has 1v.
Sensor 2: has 5v when unplugged, plugged on and back probed it has 0v.
This really baffles me as the car was running normal with no problems. It began to have a rough idle, then when parked off and started again, it just wouldnt rev at all and the idle fluctuates badly around 800-1000rpm
Im hesitant to experiment on this 1, too new for my liking. I will post the fault codes below tell me what u guys think..
Audi A4- check main plug on the ECM or same plug between components, sensors and ECM! look for corrosion, moisture, etc. Can be ECM problem but is worth it to check frist of all!?
It is to much dtcs at diferent components and sensors for all them fail at the "same time"...
Yeah all those problems at once is what made me look at the 5v ref, and i dont understand how the voltage is dropping though.. its quite unlikely that both map sensors fail at the same time.
On the other hand, i have done some research and checked these ecu's fail alot. But thats not enough proof to call a dead ecu
Have you checked the basics? Battery poles, Earth points, connectors, etc.
Establish that the battery is good and that all the main points where electricity is travelling through the car are clean and secure.
To illustrate what I mean, I had a customer come in a few days ago with a 1er which refused to start and a dash full of lights. He asked me for a new battery for the car. I checked his existing one which was fine. Cleaned the pole, the terminals and the battery tray. Plugged it all back together and the car starts and half the warning lights went away. Another one is on certain 3er's there is a common earth for all the sensors and injectors in the engine harness. The join is inside the injector harness plastic box wrapped in cloth tape. When the engine gets washed water stays in the box causing the joint to corrode and messing all the signals up for the sensors and triggering the EML. Saw an engine get rebuilt due to this wiring problem.
My point is that the cause is usually simple in nature and requires a systematic approach to diagnose. Stop looking at the computer screen full of trouble codes and look at the car. A scan tool is just that, a tool. It can't think for the technician.
Start at the beginning and work through each part of the system step by step and you can solve the problem.
Honestly i didnt check anything on the car, i was just offered a scan because the owners scantool wasnt working.
After having a good look at the log, i have asked the guy to test the 5v ref because most if not all those codes are related to the 5v circuits, and this code gave me some direction:
15373 - Sensor Reference Voltage A: Circuit P0642 00 [175] - Low MIL ON - Confirmed
On vws i have noticed if theres a battery terminal problem it almost always throws the terminal 30 dtc, im not saying u wrong - its worth the check..
I didnt ask him to check ground points either because he did check sensor grounds and there wasnt any voltage drop on the ground wires (i believe if ecu ground was bad, the sensor grounds should have a voltage drop across it..?).. again, its worth the check.
I agree about the scantool, i understand its just a guide.
Ok so i had a look at the car myself today, as i thought - the 5v circuit was shorted.
The cause of the short was from a leaking waterpump, the connector was full of water and corroded.
Unplugged the connector at the water pump, dried it abit. Started the car and everything seems to be working, no codes besides the water pumps coolant flow. Lucky doesnt seem like theres any ecu damage.
Happy with the result, my friend is happier that that ecu is not fried haha
