Codes P0123 P0420, P0300, P0302 and P0304?

Tiny
SHORTSTACK1
  • MEMBER
  • 2017 HYUNDAI ACCENT
  • 1.6L
  • 4 CYL
  • AUTOMATIC
  • 145,000 MILES
On my girlfriend ‘s vehicle I recently scanned it because the check engine light came on and it had the P0 300 302 and 304 codes as well as the P0420 codes. I have replaced the spark plugs, the coil packs both catalytic converters the upstream or bank one sensor 102 sensor as well as the crank position sensor. And I was cleaning the throttle plate on it and now it’s giving me a code P0123 on top of it it’s no longer giving me a stored code or pending code for the P0420. However, it is still running rough and it’s giving me a pending P0304 and 30302. Once in a while, but almost always a code 304. Just looking for some help on that and maybe how to get it to relearn the position of the throttle it says voltage high.
Monday, February 24th, 2025 AT 4:16 PM

3 Replies

Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 50,264 POSTS
The first codes may cause the other codes BTW. The TPS sensor is inside of the throttle body.

Here is how to change it out in the images below.

P0123 - Throttle Position Sensor (TPS) "A" Circuit High Input
P0420 - Catalyst System Efficiency Below Threshold (Bank 1)
P0300 - Random/Multiple Cylinder Misfire Detected
P0302 - Cylinder 2 Misfire Detected
P0304 - Cylinder 4 Misfire Detected

Please clear the codes once the repairs are complete. Check out the images (below). Let us know how it goes.
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Tuesday, February 25th, 2025 AT 10:26 AM
Tiny
SHORTSTACK1
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So to be sure I understand, the TPS could cause the prior codes and cause the misfiring?
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Tuesday, February 25th, 2025 AT 10:53 AM
Tiny
KEN L
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Yes, the TPS affects mixture so if the cylinder is too lean it will misfire. If you want to be sure the engine is not having an issue first, let's do a compression test.

https://www.2carpros.com/articles/how-to-test-engine-compression

Please go over this guide and get back to us.

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Wednesday, February 26th, 2025 AT 8:30 AM

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