IntroIs your Toyota Yaris D4D intermittently losing all power and going into limp mode? Had a P1121 fault code read at a garage and not sure what to do next? Read on for more information.
What is the accelerator pedal position sensor (APP) and what does it do?The function of the accelerator pedal position sensor is to convert the physical movement of the accelerator pedal (e.g. light throttle, full throttle) to a voltage signal which the ECU can understand and act upon to change fuelling and other parameters to alter the acceleration of the vehicle.
If the ECU receives a signal from the APP sensor which is out of range then it will likely log a fault code (DTC) and put the engine into limp mode where the revs will not rise above approximately a fast idle.
SymptomsOur 2003 Toyota Yaris 1.4 D-4D would intermittently go into limp mode without any warning at all. For some reason it would most often happen when driving on the motorway which is potentially very dangerous as you can imagine. This would normally happen on average once every 3 - 6 months although sometimes it would happen two or three times in one week.
After the car would go into limp mode, you could turn the engine off and on again and carry on as normal, often without issue for months. Once getting home, I would read the code using a Launch Creader 6 and it would always be P1121, I would clear this code and carry on driving as normal.
I contacted Toyota parts and was horrified to find the pedal position sensor is not sold individually and must be sold as a unit with the accelerator pedal...for £366GBPincVAT. This is absolutely outrageous for a simple potentiometer.
The P1121 code is defined here as an issue with the accelerator pedal position sensor range/performance. It's important to note that this DOES NOT necessarily mean the sensor itself is faulty and after finding out the cost of a new one from Toyota I was not about to take a gamble so I contacted a local car diagnostics specialist to test the wiring and sensor.
Considering the intermittent nature of the fault, I was not surprised when the specialist could not find any issues with the sensor, however he tested the continuity of the wiring from the plug back to the ECU and found no issues so I could at least rule that out as a possible cause.
I decided to start looking on eBay for a second hand sensor as the chances of buying a second hand one with the exact same symptoms are pretty slim. To be honest these didn't come up very regularly so here are a few other places to try (I am not affiliated with any of these and cannot vouch for their service)
How to fixReplacing the accelerator pedal position sensor on the Toyota Yaris D4D is very simple and would take even a complete novice mechanic 15 minutes. The only tool required is a 7mm spanner, one of the bolts can be undone with a socket but the other is too close to the footwell and will likely foul unless you have a very shallow socket.
1) Unplug plug by squeezing the tab and pull.
2) Undo two 7mm bolts and remove sensor.
3) Fitting is the reverse of removal!
|Pedal position sensor once removed from pedal|
Start up the car to check everything is ok and you're good to go. Experiencing similar issues? Please leave your comment below.