Engine warning light - throttle pedal?

[Tucson Ray]

Hi,

My car is intermittently producing an amber engine warning light on and using a generic code reader I get a 'P2122 - throttle pedal position sensor/switch circuit low' fault. Unfortunately I've had to reset the light with my code reader as I can guarantee the light will come on/car misbehaves when I'm no where near the dealership and I'm in the middle of nowhere! Once the fault is cleared, for the next good few days the car drives normally. I've attached some pics below.

The car is out of warranty now too.

However, yesterday the car refused to accelerate whilst driving all of a sudden and the warning light returned. This was the worst symptom the car has displayed surrounding the fault - it was actually pretty scary! So I had to reset the light with the code reader again to get me to safety.

I went to Hyundai today and luckily the master tech was working so had a chat with him about it. He says the code is recognised by Hyundai and says it's the throttle pedal. The electrical gubbins behind the pedal sound as if they're causing the problem and triggering the complaint/warning light.

He has said however this is all speculation. The worst case would be a new throttle body and you're in the realms of £1200-£1300 if it is! The car is a 2018 1.6GDI with 58K on the clock. I really hope it isn't that extreme!

Has anyone else have any experience with this? If so - what was the resolve?

[GrumpyDad]

Okay, obligatory I'm not a Hyundai mechanic, your choices are you own, I cannot be held responsible for damage, loss of sleep, or the end of the world etc. I am, however, absolutely responsible for any future National Lottery jackpot win, and shall be paid 50% of the prize money Probably best to grab a cuppa, this post is a bit of a long one...

So, as the Hyundai mechanic mentioned to you, it could be a number of things. My check list to start with would be

1. Check the wiring harness and connector where it connects to the accelerator pedal.
2. Check the wiring harness and connector where it connects to the throttle body.
3. If you have the ability to read live data with your code reader, check the accelerator pedal.
4 Check the throttle body.

So, upfront warning, when checking or doing anything that involves disconnecting and reconnecting the wiring harness, you should disconnect the battery. None of your car's ECUs will thank you for rudely awakening them with a power spike.

On the harness you are looking for any fraying of the wires, or other obvious damage. I don't know the engine layout for your model, but the throttle body on a number of Hyundai (and other manufacturers) engines is decidedly close to the radiator. In such circumstances, it is not unheard of, for the wiring connected to the throttle body to get a little too friendly with the radiator fan. The upshot being that the fan blades can cause damage to the wiring, and they can in turn lead to irregularities being reported to the engine ECU, leading to your P2122 code. The wiring behind the pedal can also become damaged, especially if there are loose carpets, or work has previously been carried out in that area.

With the connectors, you are looking for corrosion and/or dirt on the plug pins and/or sockets. Also loose wires that may not be fully connected to the pins of the plug. Contact cleaner can help with corrosion and dirt. Loose wires may be a case of removing the affected pins from the connector (using the appropriate extraction tool) and crimping on a new pin, or possibly splicing on a new connector.

If your code reader and accompanying software can read live data, you may be able to test the pedal. (I'm a big fan of Torque Pro (Android), but I haven't got around to hooking it up to my Tucson yet, so I don't know what data is generally available.) If you can read live data, you will likely find the appropriate data under the engine ECU, and you are looking for "Accelerator Pedal Position" (which should read as a percentage), "Accelerator Pedal Position Sensor 1 - Voltage", and "Accelerator Pedal Position Sensor 2 - Voltage". (These are different to the throttle sensors, so be sure to find the correct readings.)

With the ignition on, but the engine off, you should be able to take readings from the accelerator pedal. The position (%) should be reading 0 when not pressed, and 100 (or very close, so 99.4 is near as makes no difference) when fully pressed. No prizes for guessing what it should read when the pedal is pressed about half way.

The position sensor voltages should increase when the pedal is pressed, and their increase in voltage is position dependent; so it will read lower at 50% pedal than at 100% pedal. If you do test this, write down the voltages you get at different pedal positions (say 0%, 20%, 50%, 75%, and 100% to get a good range).

The voltages on the two sensors will be different. On the presumption that Hyundai follow the normal pattern (I'm new to Hyundai, so I don't know yet), the voltage on APP sensor 1 will be twice the voltage on APP sensor 2 (+/- 50mV). This is done so that the ECU can validate the signals coming from the two sensors. If it doesn't get the expected difference between the sensors, then it throws up a warning. HOWEVER, I want to stress that I don't know whether Hyundai use the APP1 = APP2x2 method. So if the value of sensor 1 isn't double that of sensor 2, don't automatically decide it is the pedal; check with your Hyundai mechanic (who should be able to tell you from the figures you collect from the test if the pedal needs replacing).

If all that fails to turn up the culprit, the throttle body itself can cause a P2122 fault if it isn't operating correctly. If the butterfly valve inside, for example, isn't shutting fully, or a build up of grime inside has occurred and is stopping free movement. But to check that involves removing the throttle body, and so that one should definitely be left until the other options are checked and discounted.

Hopefully this gives you a starting point for diagnosing the problem. Obviously, only undertake diagnostics and repairs you are comfortable and confident in your ability to do.

It's difficult to say what the best (read "Cheapest") fault would be (actually, it isn't, the answer is you should be hoping for dirty connectors, but I wouldn't count on that being the problem). If it is one of the APP sensors, they might be replaceable, but I have no clue what Hyundai charge for the sensors, or if they are actually individually replaceable. Of course, it may be easier to check a local breaker for a replacement pedal unit. There are Mk3 Tucson accelerator pedals on eBay for £20 - £30, as a rough idea on cost.

Obviously a new OEM pedal is going to be a lot more expensive. SG Petch is currently listing an accelerator pedal for a Mk3 1.6 GDi at £273.82 +VAT & shipping (not fitted).

The least likely option is probably the throttle body being beyond repair; in which case you are looking at roughly £40-£50 for a used one. For a new OEM part, SG Petch is currently listing a throttle body for the MK3 1.6 GDi at £292.30 + VAT & shipping (not fitted). Plus a couple of quid for the replacement bolt and nut to go with it (because new mounting hardware is worth getting if you have to replace it).

Of course, the labour charge for having an Hyundai (or any) mechanic fit either of them, or to sort a wiring problem, is likely to be significant. Plus, if you are having a mechanic do the work, they aren't going to want you to supply the part. A lot of people worry this is so the mechanic can fleece them on the part cost, but that is rarely the case. It is usually about quality assurance, and the fact that they will have to cover that repair in the event that the replacement part has a further fault. If you supply the part and it has a problem, it complicates the situation, a lot. At least if you have a rough guide on part price, however, you'll know if the repair quote for the part is outlandish.

So, good luck with tracking down the source of your error code, and here's hoping it is something relatively easy and inexpensive to correct.

[Indalo]

the labour charge for having an Hyundai (or any) mechanic fit either of them, or to sort a wiring problem, is likely to be significant. Plus, if you are having a mechanic do the work, they aren't going to want you to supply the part.

A belated welcome to the forum, ‘GrumpyDad’.

Your assessment of the OP’s issue and the diagnostic methodology are excellent but even if the OP is familiar with the level of faultfinding required, not to mention the contortions required to access the various components, I’d recommend that he/she bites the bullet and places the car in the hands of a Hyundai dealership.

The equipment available to KIA workshop staff is far superior to that available to the general public and is also backed up by TSBs and other assorted information which simplifies the process of identifying the root cause.

Obviously, no-one wants to face a bill that includes a punitive diagnostic charge but unless the OP is well-versed in vehicle electronics and can manage his daily life with the car off the road for a few days or even weeks, a franchised dealer is more likely to sort the matter than an independent garage. There are some specialist auto electricians around who, in my experience, are excellent at faultfinding but unearthing one prepared to be dragged away from his lucrative bread-and-butter work of fitting trackers, cameras, alarms, and satellite dishes, much of it in commercial vehicles and motorhomes, might prove challenging.

[Tucson Ray]

Thank you @GrumpyDad and @Indalo - both responses providing fantastic feedback.

I have since had further conversations with the dealer and once the festive period is over - the car will be going in to start the diagnosis and repair.

Fingers crossed the fault is found with ease and the cost to repair is even easier on the wallet!

Will keep you posted - thanks!

[Tucson Ray]

A little update for the thread as the car has now been diagnosed by the dealer and I now know what's upsetting it.

So it has been confirmed as the throttle pedal and it needs renewing. Part number from Hyundai is 32700D7800 and isn't cheap! Certainly not on top of the service, MOT and air con service happening as well.

Car goes it Monday 26th and should be turned around in a day. Fingers crossed it needs nothing for the MOT now!!!!!!!!!!!!

Anyway - hoping this helps someone out there who might be in the same situation.

[Berty]

Those accelerator assemblies aren't expensive at all, labour is likely the culprit. You can pick them up used online and fit them yourself with a 10mm bolt and attaching the electrical assembly, it takes minutes.

I changed my own in my 2023 but not for part failure. I wanted to update my non n-line pedals to n-line pedals. I'm sure I paid around £70 shipped OEM new from Korea for an N-line one but a replacement black(non nline) part number would have been around £50. There are lots for sale online because the Hyundai and Kia share the same part numbers.

If there are more electrical gremlins rather than just the pedal itself then likely best leave it to the dealer.