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Discussion Starter · #1 ·
I've search everywhere on the forums, even google for that matter, about the P2121 and I can't seem to find an answer to my problem. No other code, just P2121 intermittently and the DWB portion of the throttle body is dead. If I turn the car off and on it usually works again, especially if I clear the codes before turning it off.

I have gone through the full troubleshooting:

  • Check continuity between E2 and negative terminal of battery, solid.
  • Check continuity from APPS to E4 connector on ECM for VPA, VPA2, E2 & VC. All solid & no shorts between any of them.
  • Check voltage on VC, VPA and VPA2 with ignition on but not cranked, all were in spec. VC was a steady 5V. Don't remember the exact voltage readings, but VPA was in the .3 to .9 range released and 3.2 to 4.8 depressed. VPA2 was between 1.8 to 2.7 released and 4.7 to 5.1 depressed.
  • Found APPS connector to be brittle and broken. Replaced with new connector, pulled pins from old connector and inserted into new connector, did not solder in a splice.
  • Check throttle control motor wires for an shorts or loose connections. Didn't find any.
  • Found throttle control motor connector to be brittle and broken. Removed pins from connectors and inserted onto pin individually. Waiting for new connectors.
  • Check voltage readings on throttle position sensor with ignition on, but not cranked. VC was steady 5V. VTA to E2 was around .65V. VTA2 to E2 was around 2.39V.

*I will check voltages again tomorrow and record actually values, along with recording the resistance on the all 3 throttle sensors/motors.

P2121 is the only code that keeps getting thrown, so I don't think it's anything else buy I figured it wouldn't hurt to check them anyways. The fact that all the voltage readings are within specs makes me think the sensor is not actually faulty. I don't really want to spend $250 or whatever on a new one for the same issues to happen.

Earlier I took it for a test drive after finding the broken connectors and checking all the voltages and continuity. After 4.5 minutes it threw the code and I lost DWB. Pulled over, read the code. Sure enough P2121. Clear the code, turn the car off, wait a few seconds and turn it back on. DBW works perfectly. So I keep driving around for another 30 minutes without ever having any issues. Flooring it, driving like a granny, feathering the throttle, holding steady throttle positions are different points , turns, rough roads, hard braking. You name it, I tried it. Doesn't seem like there are any loose connections or bare wires that could short. Doesn't seem like there are any dead spots in the APPS.

Does anyone have any ideas on this or other things I should check or look for? The fact that it is intermittent is driving me insane. I think I have the issue solved and then it pops back up randomly. Makes me thing it's a short somewhere but I can't locate or replicate it. Apologies if there are any mistakes in the wall of text, I am tired and annoyed.

Thanks!
 

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2004 Lexus IS300
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I've search everywhere on the forums, even google for that matter, about the P2121 and I can't seem to find an answer to my problem. No other code, just P2121 intermittently and the DWB portion of the throttle body is dead. If I turn the car off and on it usually works again, especially if I clear the codes before turning it off. I have gone through the full troubleshooting:
  • Check continuity between E2 and negative terminal of battery, solid.
  • Check continuity from APPS to E4 connector on ECM for VPA, VPA2, E2 & VC. All solid & no shorts between any of them.
  • Check voltage on VC, VPA and VPA2 with ignition on but not cranked, all were in spec. VC was a steady 5V. Don't remember the exact voltage readings, but VPA was in the .3 to .9 range released and 3.2 to 4.8 depressed. VPA2 was between 1.8 to 2.7 released and 4.7 to 5.1 depressed.
  • Found APPS connector to be brittle and broken. Replaced with new connector, pulled pins from old connector and inserted into new connector, did not solder in a splice.
  • Check throttle control motor wires for an shorts or loose connections. Didn't find any.
  • Found throttle control motor connector to be brittle and broken. Removed pins from connectors and inserted onto pin individually. Waiting for new connectors.
  • Check voltage readings on throttle position sensor with ignition on, but not cranked. VC was steady 5V. VTA to E2 was around .65V. VTA2 to E2 was around 2.39V.
*I will check voltages again tomorrow and record actually values, along with recording the resistance on the all 3 throttle sensors/motors. P2121 is the only code that keeps getting thrown, so I don't think it's anything else buy I figured it wouldn't hurt to check them anyways. The fact that all the voltage readings are within specs makes me think the sensor is not actually faulty. I don't really want to spend $250 or whatever on a new one for the same issues to happen. Earlier I took it for a test drive after finding the broken connectors and checking all the voltages and continuity. After 4.5 minutes it threw the code and I lost DWB. Pulled over, read the code. Sure enough P2121. Clear the code, turn the car off, wait a few seconds and turn it back on. DBW works perfectly. So I keep driving around for another 30 minutes without ever having any issues. Flooring it, driving like a granny, feathering the throttle, holding steady throttle positions are different points , turns, rough roads, hard braking. You name it, I tried it. Doesn't seem like there are any loose connections or bare wires that could short. Doesn't seem like there are any dead spots in the APPS. Does anyone have any ideas on this or other things I should check or look for? The fact that it is intermittent is driving me insane. I think I have the issue solved and then it pops back up randomly. Makes me thing it's a short somewhere but I can't locate or replicate it. Apologies if there are any mistakes in the wall of text, I am tired and annoyed. Thanks!
Yea that happened to me as well. I had the same code and it would work intermittently like you described. It was the APPS sensor. I have read that the connections inside break overtime and you could resolder them. I bought a new sensor but you could try that first before spending $250. Here is a link where someone shows how to do it.
 

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Discussion Starter · #3 ·
Yea that happened to me as well. I had the same code and it would work intermittently like you described. It was the APPS sensor. I have read that the connections inside break overtime and you could resolder them. I bought a new sensor but you could try that first before spending $250. Here is a link where someone shows how to do it.
Yeah I saw that video, not the type of fix I would do. I don’t like having broken parts even if it functional and unseen. It’s just weird that the issue can’t be replicated during testing and is so intermittent. Guess I might have to bite the bullet and buy a new APPS. Thanks for the help
 

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I will have to confirm which code I was getting, but before I took my car down for repair I was receiving a similar TPS code and intermittency mirroring what you describe.
I've tried with three different TSP sensors and they all have the problem.
One person I spoke with said that the "square type" pins in the connector start to deform and loosen causing intermittent connection. I haven't gone back to reinvestigate but I will have to when I get there in my rebuild.
You may want to check that and see how the pins on the connector look, depending how you were performing your diagnostic (unplugging the sensor/actuator or not, etc.).
 

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Yea that happened to me as well. I had the same code and it would work intermittently like you described. It was the APPS sensor. I have read that the connections inside break overtime and you could resolder them. I bought a new sensor but you could try that first before spending $250. Here is a link where someone shows how to do it.
If the solder breaks down you can bake them to reheat the solder as a temporary fix. Hook up some sort of monitering to the tps output and drive around and see if it goes out of range as you drive around.
 

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Hi, maybe this can give you insight on the issue as I also had p2121 and occasionally p2127. you can also view my threads on them. also, i don’t have the link but there is another guy that goes by (peter_wagon, i think) that also had this issue. so, i was battling the intermittent issue of losing throttle since last year. first, i replaced the APPS thinking it was it, but it wasn’t. i saw that my connector to the APPS was soo brittle so i bought a new pigtail from (wiring-specialty) and had my friend solder on the connection. it fixed it for a while until it popped back up months later into 2022. so, i revisit ALL connectors. at this point I saw that the connector on the throttle control motor was bare….soo, i then bought a new (used) throttle body. now..after it went on, it was like 50/50 on having full throttle and having like 50% throttle. it was so weird because I had the issue pop up everytime i did a cold start. the codes i was getting was p2121 and p2127. nearly a year after i switched out my throttle connector for the APPS and replaced the throttle body, i figured i’d do ANOTHER look at my connectors because I was frustrated. I checked the connector TO the throttle control motor and boom. it was brittle and falling apart. so, bought a pigtail for that from the same place, spliced it on, and now i was content. until, i saw that it was still throwing p2121 only. to end this, what finally did it was my friend and looked at the splicing for the connector to the APPS (from a year ago) and saw that the soldering was done poorly. we changed it up and made a more secure connection and i believe almost 300+ miles, no more throttle code.

to make this short:
  • check all connections on the throttle (APPS, TPS, and TCM) to and from the ECU.
  • if your connectors are good, check the sensors for the TCM or the APPS.
-if you are going to pigtail on a new connector, please have a good and secure connection when you splice.
 

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Discussion Starter · #7 ·
Hi, maybe this can give you insight on the issue as I also had p2121 and occasionally p2127. you can also view my threads on them. also, i don’t have the link but there is another guy that goes by (peter_wagon, i think) that also had this issue. so, i was battling the intermittent issue of losing throttle since last year. first, i replaced the APPS thinking it was it, but it wasn’t. i saw that my connector to the APPS was soo brittle so i bought a new pigtail from (wiring-specialty) and had my friend solder on the connection. it fixed it for a while until it popped back up months later into 2022. so, i revisit ALL connectors. at this point I saw that the connector on the throttle control motor was bare….soo, i then bought a new (used) throttle body. now..after it went on, it was like 50/50 on having full throttle and having like 50% throttle. it was so weird because I had the issue pop up everytime i did a cold start. the codes i was getting was p2121 and p2127. nearly a year after i switched out my throttle connector for the APPS and replaced the throttle body, i figured i’d do ANOTHER look at my connectors because I was frustrated. I checked the connector TO the throttle control motor and boom. it was brittle and falling apart. so, bought a pigtail for that from the same place, spliced it on, and now i was content. until, i saw that it was still throwing p2121 only. to end this, what finally did it was my friend and looked at the splicing for the connector to the APPS (from a year ago) and saw that the soldering was done poorly. we changed it up and made a more secure connection and i believe almost 300+ miles, no more throttle code.

to make this short:
  • check all connections on the throttle (APPS, TPS, and TCM) to and from the ECU.
  • if your connectors are good, check the sensors for the TCM or the APPS.
-if you are going to pigtail on a new connector, please have a good and secure connection when you splice.
I didn’t cut the wires out, I removed the pins from the old broken connector and repin into the new connect. Did the same thing for APPS and the TCM. I ended up replacing the APPS with a new OEM one of eBay and it fixed all the issues so far. Not sure how many miles have been driven since it’s but sisters car, but she hasn’t had any issues in about a month.
 
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