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Discussion Starter #1
Hi everyone, I`m brand new here. For 3 months I have been battling with this dreaded error, reading forums, watching youtube videos and I can't fix it. The car runs on low rpm (900) when cold and on high when hot (1200). I started by cleaning the throttle body very well. Still same error. Then I bought another used but told to be working throttle body off ebay, replaced it. Still the same error. I cleaned the Air Control Sensor with a spray for sensor cleaning, plugged it, wiped the error codes with my OpCom, and suddenly it worked fine - started with normal high rpm, and when the engine went hot, it dropped down to the normal 900, 950 rpm. But that correct condition lasted for 2 minutes and the error code returned.

My problem is I don't really understand where to look anymore. Here are 3 of my questions that I need help with:

1. I can't find what the correct readings should be from the Air Control. When idle, with running engine, the Throttle Position sensor reads 4.4V, but reading online it seems it should be 0,5V? What is the correct Voltage for Idle Throttle Position on this engine model?

2. Is it normal that when I press the throttle pedal that Throttle Position sensor starts at 4.4V and then goes down? Is that how the sensor should be working? Somehow intuitively I think it should go up in Voltage?

3. Also I`m reading I should somehow reset or relearn the ECU with the new settings after replacing the Throttle Body. Is that true and if yes, how to do that with the OpCom ? I`ve read online it's somewhere in the "Special Functions" tab, but there I only have 2 buttons - "Reset Idle Adjust" and "Reset Init Coding".

Can anyone give me advice where to look next? Thanks a lot in advance! Let me know if you want screenshots and specific readings from the OpCom.
 

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That's the right way round,here's the data spec and a graph from a running engine
Untitled picture1.png
Untitled picture2.png
 

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Discussion Starter #3
Thank you! Hmm that's interesting. I recorded all the info from my Op-Com. The pictures are all the measuring blocks with running engine. The error code I get is:


Total number of fault codes: 1

P0505 - Idle Air Control Voltage High
(01) - Present


Then I cleared the errors, and unplugged the cable from the AirControl Flow - the thing that measures the air comming in the Drossel Body (sorry I`m not sure how it's called, I guess it's IAC - Idle Air Control?)

Then I get these errors with the running engine:

Total number of fault codes: 2

P0100 - Mass Air Flow Sensor Voltage Low
(04) - Present

P0110 - Intake Air Temperature Voltage High
(04) - Present

Notice that the P0505 error is not present at this stage.

Then I plugged the AirControl cable back and unplugged the cable from the Drossel Body and I now get these errors:

Total number of fault codes: 2

P0120 - Throttle Position Sensor (TPS) Voltage Low
(04) - Present

P1515 - Idle Speed Actuator Feedback Open Circuit
(04) - Present

Reading here: https://www.obd-codes.com/p0505 , it seems that it's most probably the IAC that needs replacement

Any advice? Thanks!
 

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"Red One.."
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You have 7 wires going to the throttle body on your car. 5 of these wires are for the two separate position sensor tracks (two pairs of wires in from the ECM & a signal ground) - these two sensors work as Valer has shown above, they always work in reverse to one another, so as one starts low voltage and climbs up with throttle position, the other starts high and drops down. That's the ECM's way of error checking to make sure the signals are correct.

The remaining two wires are for the feed and earth to the actual motor attached to the throttle plate - it's this side of the circuit that P0505 relates to. The checks for this involve checking those two wires from ECM to throttle body, for short to ground, break in the wires, short to voltage etc...if the wiring is okay it leads to either a fault with the throttle body (ruled out if you've replaced this already), or the ECM.

I have seen ECM's failing with this fault beforehand many moons ago, so it is entirely possible this is the root cause. You'll need to ensure those two wires (pin 6 & 7 into the throttle body connector) are good, and also have 12v feeds and earths into the control unit checked to confirm correct diagnosis.

The other codes you've noted are obviously due to the components you've unplugged, so can be disregarded.

A copy of the wiring diagram that confirms the area to focus on:

Screenshot 2016-11-19 19.58.04.png
 
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Discussion Starter #5
Hi Nick! That's a great info!!! Thanks!
Before I check the wires, from the diagram above I understand that pin 4 is ground right? If not how can I best measure the voltage to either pin 6 or 7 ? Should I measure between ground (somewhere in the car) and the pins one by one and see which one is the 12 and which is ground?
 

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"Red One.."
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Pin 4 is the ground wire yes, but only the reference ground for the two sensor/feedback circuits, so it can be discounted in this case as it's not directly related to the actual motor for the throttle flap.

As above, Vauxhall's check procedures involve you disconnecting both the ECM/throttle body and measuring each wire end to end individually (so terminal 7/61 and terminal 6/45) for the following: short to ground (measure each wire against earth for continuity/resistance) short to voltage (measure each wire against earth for voltage) and open circuit (measure each wire end to end for continuity/resistance).

Note that when you're probing into the end of the ECM plug with the last check to be very careful what you use so that you don't damage the pins - a fine terminal or even just some bared back wire. If you need a pin assignment for the ECM plug I can look that up tomorrow.

In real world terms the best test method is by means of voltage checking with the circuit connected up, as it's in it's correct working state and the circuit is under load. Ideally probing with an oscilloscope will show up the voltage/earth down those wires and be easy to visually see a glitch in the circuit that opens and shuts the throttle plate - this might not be an option as it involves the right kit, so I'd at least stick with the wiring checks above to begin with.
 

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Discussion Starter #7
Thanks again Nick! Ok so here is what I measured:

1. I unplugged the cable from the throttle body, but still haven't unplugged the other side of the cable from the ECM. It's kind of hard to reach so I will do the open circuit test as a next step, but I found something strange:
2. I measured for voltage between ground and pin 6 - what I get is 5.5V
3. I measured for voltage between ground and pin 7 - what I get is 0V
4. I measured for continuity between ground and pin 6 - and I get a short signal
5. I measured for continuity between ground and pin 7 - and I don't get anything

That doesn't sound normal so far right ?
What I was expecting to get is 12V on Step2 and No shortage in Step4. Is that correct ?
 

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"Red One.."
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That may well be correct yes. The trouble with testing voltage at either pin is you're not going to know 100% what the voltage is supposed to be, as when that circuit is operating normally the voltage is varied in order to vary the angle of the throttle plate.
 
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