P1342 Ford Transit Throttle Pedal Circuit Fault.

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P1342 Ford Transit Throttle Pedal Circuit Fault.

Postby Technician » Sat Mar 05, 2016 7:42 pm

Hi guys,

I have a Transit 2003 (ABFA) that intermittently raises its own idle speed to approx 1500 rpm, when I turn off the engine and restart the idle speed is normal again. I have carried out a code read to receive the code above and completed a road test with the scanner connected to record some live data, believe me the van drove perfect and recorded no faults, the idle speed did not increase at all, I could not believe it. Anyway I have looked at the data for checking this throttle pedal circuit and it seems the tech info only provides resistance checks and voltage tests, but what I want to carryout is a dynamic test of the pedal using the scope, but I have no good known comparison waveform, can anyone help with this please!

I am to believe (not checked it yet) that the throttle pedal has three circuits, and the code above is referring to the A circuit.

Thanks for any advice. :D

Removed this section now moved "Help fix my car thread". Sorry posted incorrectly.
Last edited by Technician on Sun Mar 06, 2016 5:46 pm, edited 1 time in total.
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Re: P1342 Ford Transit Throttle Pedal Circuit Fault.

Postby tangoman » Sun Mar 06, 2016 1:31 am

This should be a easy Circuit to test you don't need a wiring circuit to check but this might help you I also tap the pedal when I scope the pedal when checking with scope you don't want to see any drop outs when you scope it but don't forget if you do have a drop out before you go and out in a new pedal check the power and grounds to the pedal . I have seen a few pedals replaced only to find the ECU was not giving the pedal 5 volts
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Re: P1342 Ford Transit Throttle Pedal Circuit Fault.

Postby Martyn » Sun Mar 06, 2016 10:50 am

Moved as requested.
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Re: P1342 Ford Transit Throttle Pedal Circuit Fault.

Postby FioranoCars » Sun Mar 06, 2016 12:33 pm

Hi Technician
I can't help on this specific application, but fly by wire throttles we do see a lot, most have 2 circuits for plausibility and redundancy - to be sure the input is valid!

Most, but not all, of the dual circuits work in inverse so (and using Tangoman's circuit as the example - which shows it set up this way with opposing sliders on the potentiometer) - I'll simplify by saying 0.5 to 4.5v but this might be 0.3 to 4.8v, or something else, and might be not inverse, both might be rising, however the picture shows a common supply, so lets expect a directly proportional inverse. So here you go:

- Output A = 0.5v at idle and 4.5v at WOT - Pin 1 at pedal, Pin 10 at the ECU
- Output B = 5v at idle and 0v at WOT - Pin 5 at the Pedal, Pin 29 at the ECU

Your pedal (if this is the correct wiring for your vehicle) has another 2 circuits, that are ground switched to show Idle and WOT:
- WOT - PinB at Pedal / Pin 30 at the ECU
- Idle - Pin D and Pin 8

So 4 Circuits ... Assuming you have a 4 channel scope I'd personally check at the ECU first, as this validates the wiring harness, and then recheck at the Pedal - but access might be an issue and therefore going to the pedal might be more pragmatic in this instance, so I'll explain what my approach would be...

1st test - at Pedal for ease - Key On, Engine off - We'll assume that the ECU supply (pins 33 and 30/8), wiring and earth (51/50) are good for now.
Timebase - 500ms/div / Sample 50ks
ChA - +/-5v - Pin 1 - expect near zero volts at idle rising to near 5v at WOT
ChB - +/-5v - Pin 5 - reverse of Channel A 5v dropping to 0v
ChC - +/-20v - Pin D - Idle switch - expect circa 0v at idle and 5v (might be 12v or 1v) when not
ChD - +/-20v - Pin B - WOT switch - expect voltage (similar level to ChC when not at idle) until WOT when it should be reduced to 0v
Make sure you use a Chassis earth on one channel - not Pin 3 or pinA or PinC!
+ Create a maths channel to be A+B - this should show an almost flat line at circa 5v, critically, it's going to be almost dead flat, and much easier to see incongruous data as spikes here, and this is in effect what the ECU is doing to valid the two position readings. If you had a dual rising signal you could attempt to create a flat line comparison using a maths channel like this, for say a 5v chA and 2.5v chB = "A-(2xB)" or even some offset adjustment "A-(2x(B+0.2))" but you'd need to play with this!!

Start the scope capture and then at various speeds of pedal movement - from slow and steady and slow steady release, to rapid snap, depress the accelerator pedal several times. Some part depression and release, might help if the problem needs to be provoked, but start off with simple full open and release.

This will get you a very quick idea of the function of the Pedal, and provided the chance to adjust the scales, arrange the data/scaling to give a screen that you can analyse. If ChA/B are "over limit" then change them to +/-20v

If the ChC and D appear to be working, then I'd drop them and re-use the channels to study the earth and supply of the potentiometer:
ChC - +/-5v - Pin 4 - ECU Supply +5v should be expected (again might be over limit so +/-20v)
ChD - +/-1v - Pin 5 - Earth 0v over very close

Retest, and see if these values have any "issues" (drops/spikes) that correlate to any "issues" at channel A or B

If you see nothing after either of these tests with engine off, the try repeating the test engine on, or in deed on a road test.

Personally I'd then clean and VISUALLY inspect all the connectors with contact cleaner and GEL then with a dielectric gel (Pedal, ECU and any other joints between the two) and retest, we see lots of issues due to high resistance on connectors, or with wires pulling at the pins from mechanical strain - being kicked etc!

At this point if you still don't see any "issues" then retest at the ECU pins, which will also test the wiring harness and show a more realistic picture of what the ECU is seeing (possible signal being earthed due to wiring issues etc).
ChA - +/-5v - Pin 10 - expect near zero volts at idle rising to near 5v at WOT
ChB - +/-5v - Pin 29 - reverse of Channel A 5v dropping to 0v
ChC - +/-5v - Pin 33 - ECU Supply +5v should be expected (again might be over limit so +/-20v)
ChD - +/-1v - Pin 51 - Earth 0v over very close
Again earth one lead to chassis, not an ECU earth.

Attention to volt drop verse the pedal readings taken earlier, especially on the earth and supply ...

Of course most modern diagnostics tools would allow a rapid solution by doing a "recording" of the values that it (the ECU) is seeing -both the throttle pedal parameters and both switch status ... which is where I would have started, but it's not as much fun as getting the scope on the car!!

The Diag Tool would not confirm if the fault was the ECU 5v output (ECU rebuild/renew), or a poor earth (probably the external earth connection, but could be internal to the ECU), or the Pedal verse the wiring. BUT would have given you some guidance and help as to what elements needed to be focussed on.

HTH, but please post your results!

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Re: P1342 Ford Transit Throttle Pedal Circuit Fault.

Postby Technician » Sun Mar 06, 2016 6:14 pm

A very BIG THANK YOU to Martyn for moving the post, and to tangoman and Fioranocars for posting your replies and including diagrams, it is very much appreciated. I have printed the information from both of you to help me work through the fault.

A couple of things to say;

The van has been driven again today, I completed two separate road tests, the first road test did not produce any evidence of a fault, the second road test did show an increase in the idle speed at just over 1000 rpm, at 500 data cycles a permanent fault code was stored P1342. Interestingly the EML warning lamp does not illuminate to indicate a code has been set, maybe the bulb has failed or somebody has disconnected it, another job to look at I suppose.

I will not be using the pico scope at this time to investigate this fault, pico is brand new to me and have zero experience using it, hence working on a faulty vehicle with serious unfamiliarity of equipment is a serious receipt for a disaster, so better to stick with what I know until I am comfortable using the pico scope.

I'll assume then that the shape of the voltage graph from the throttle pedal will start at approx 1V producing a positive slope until a maximum voltage V is reached and then a gradual negative decrease in voltage V until approx 1V has returned. I can mentally see the shape of the graph but can't produce it here for reference.

I will post the conclusions when I complete the job. Thanks. :)
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Re: P1342 Ford Transit Throttle Pedal Circuit Fault.

Postby FioranoCars » Sun Mar 06, 2016 7:04 pm

Hi Technician
This one should be straight forward for the novice and a scope, especially at the pedal, so don't be too fearful, you can even start off using a template from the automotive menu, under the "Accelerator Pedal" then "Analogue - Analogue", the basic settings for the scope will be setup for you, just copy them to the other channels.

My only suggestion is to "back pin" rather than piece the wires, as you'll need to get to the connectors to clean them, may as well get some readings before and after, to prove to yourself and the owner that the issue is/is not related to high resistance ... you've got to start somewhere and this is fairly straight forward. I doubt this vehicle uses Pulse Width Modulation output, especially from the diagram, but if it does, just post a saved file, and someone will help explain how to create a frequency maths channel to "display" the value in a easy to review format.

The EML will only light up for an "Emissions" related event, it's not really an "engine" light, it can only be used to report emissions, and TPS can fall under this, but not for your current fault.

You can check the bulb at Key On, as it should light up during self test, then turn off once the engine has started. If not illuminating at all, then I would suggest that the bulb or wiring is compromised. We see a lot of mid 80's to early 90's cars that have been worked on without the correct tooling, and the bulbs are removed to avoid the proper resets or worse, leave the car is a permanent state of fault!

HTH, and have courage!

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Re: P1342 Ford Transit Throttle Pedal Circuit Fault.

Postby Technician » Fri Mar 11, 2016 9:32 pm

Might get another chance tomorrow afternoon to have another look at this van hopefully. The van has not displayed anymore of the symptoms since I last posted, a bad electrical connection "maybe" but I would have thought a faulty pedal/ECM after a longish run would show up the fault fairy often but nothing at all since I was last here and the van is used everyday. Maybe a glitch in the system!
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Re: P1342 Ford Transit Throttle Pedal Circuit Fault.

Postby FioranoCars » Sat Mar 12, 2016 12:25 am

Glitch, spurious, quite possible!
but regularly we find small, often beyond visual identification, high resistance (oxidisation etc), that can throw errors, in fact a Aston Martin Rapide MY2011 a couple of weeks ago, was giving various throttle body, and pedal errors, all down to the pedal connector. Sadly the connectors were cleaned before the scope came out, and the problem was solved. So no captures to offer, but clearly the ECU's can be very fussy about the data and it's plausibility.

I'm sure that these faults often end up with rapid "spitting of bits" (new pedal potentiometer etc) based on errors codes when it's really wiring and connectors in the harsh footwell environment that create more issues...

Please post any data and codes, be interested to see how it pans out

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Re: P1342 Ford Transit Throttle Pedal Circuit Fault.

Postby STC » Sun Mar 13, 2016 8:40 pm

Technician
In the event of Pedal Failure, I have seen many different systems, particularly Diesels that raise the Engine Speed to 1500 rpm. That is a feature within the controller to help you get parked safely, onto a recovery truck ..........

Richard
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We have met several times, way back in Hayes :oops: (What a pigs ear that has become) and in your current location, it has been a while. I believe Abi & Luke are still with you ? I will drop you a line, may be good to catch up. Had no idea that you had such a thorough understanding of this side of things.

Indeed the 2 tracks will never output the same voltage, rather as you say, one may be inversed, one may be PWM & the other analogue, one will be half the other ..... Not forgetting that there may be temperature compensation in there too.

The ECU will be VERY fussy when it comes to Pedal Data Plausibility for reasons of safety.
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Re: P1342 Ford Transit Throttle Pedal Circuit Fault.

Postby Technician » Mon Mar 21, 2016 10:28 pm

No more news just yet unfortunately, the van runs OK every day at the moment, however I take on board what STC has mentioned, and that is temperature, it seems that this fault occurs in colder conditions rather than warmer from recent experiences. I don't feel that unless the idle speed has increased and stayed there indicating that the fault is present that there would be any meaningful data to collect, so will just have to ride it out I suppose, but I will post the findings when it occurs. Just thought I'd pop in to let you guys know what is or is not happening at the moment with the fault.
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