P1123
HyundaiThe Powertrain Control Module (PCM) detects that the throttle position sensor (TPS) signal voltage is within its operational range, but its value is consistently higher than the expected voltage for the current engine operating conditions.
Medium SeverityThis code means your engine computer is getting a bad signal from the Throttle Position Sensor. It thinks the throttle is more open than it really is. That'll throw off your fuel and make the engine run like crap.
⚠️ Before You Begin (Safety First)
Don't ignore this. A bad TPS can make the thing jump or just die on ya. Always work on a cold engine and pull the battery cable before you touch anything electrical. Keep your fingers out of the way.
Common Symptoms
- Runs rough
- Don't wanna go when you step on it
- Hiccoughs when you try to accelerate
- Check Engine light is lit up
- Trans might shift funny
Common Causes
- Bad TPS
- Wires all messed up or corroded
- Throttle body gummed up, sticking open a hair
- Or the computer itself is fried
Frequently reported on: Hyundai Elantra (2001-2006), Hyundai Sonata (1999-2005), Hyundai Santa Fe (2001-2006), Hyundai Accent (2000-2005)
Diagnostic Steps
- Get your scanner out and watch the TPS voltage. See what it's doing at idle and full throttle.
- Pull that TPS connector. Look for bent pins or rust. Clean it up good.
- Follow the wires from the TPS all the way back to the computer. Make sure nothing's chafed or busted.
- Get some throttle body cleaner and a rag. Clean out all that carbon crud around the throttle plate.
- Grab a multimeter and test the TPS. See if the voltage changes smooth when you move the throttle by hand.
- If all that's good, you're probably looking at a new TPS. Slap it on and clear the code.
👨🔧 When to Call a Professional
If you've poked around the wires and cleaned the throttle body, and that light still comes on, get it to a shop. Sometimes it ain't the sensor, it's the computer. Don't just start swapping parts if you're guessing. You'll waste money.
Commonly Asked Questions
Can I drive with a P1123 code?
You can, but it's gonna run like crap and might leave you stranded. Get it fixed.
What's "higher than expected" really mean?
It means the computer thinks the throttle is open more than it actually is. Not totally broken, just off.
How much for a new Throttle Position Sensor?
Parts ain't too bad, fifty to a hundred bucks usually. If you do it yourself, that's all you're out.
Can cleaning the throttle body fix it?
Maybe. If the throttle plate is sticky and don't close right, the TPS reads wrong. Always clean it before you buy a new sensor.