Does anyone happen to know the function, or expected voltage measurement, of the round plug on the passenger side of the TB?

I recently repaired a vacuum leak coming from the bottom plastic breather hose off the TB, and after putting everything back together, I’m getting the p1229 code with engine restriction and a slight bounce to my idle.

I’ve attempted to disconnect, clean, and reconnect all TB connections, but nothing changed. I then unplugged, and reconnected, each cable individually while the car was running, and the only plug that did NOT provide any idle change when disconnected was this round plug, so I assume this is the culprit of my problem. I’m hoping to test the cable voltage to check if I damaged the cables during my vacuums leak repair, or if that component of the TB itself is done for.

 

The throttle motor is already disconnected by the ECM.
When you unplugged it, the ECM already had it 'switched-off-VIA-the-relay'.

P1229 Throttle motor control circuit malfunction


Throttle motor disconnected
Throttle motor to ECM drive circuits short
circuit or open circuit
Throttle motor failure

When RED MIL is activated
(DTC logged; first trip), ECM:
– Switches off throttle motor
(via relay)
– Initiates throttle “limp home”
mode: engine speed controlled to
between 1000-1250 rpm by fuel
cutoff to cylinders
– Inhibits idle speed control
– Inhibits cruise control
– Inhibits traction control / stability
control

 

Ahh duh, that makes perfect sense because after initial reassembly, I was able to successfully drive for about 30 seconds before this happened.

Well any suggestions on what else I can test, or am I pretty much stuck with trying a new TB? The vacuum leak repair was an attempt of solving stuttering during heavy acceleration. Could you see a correlational between a bad TB and stuttering?

 

watch the video you will have your answers

 

Good (and very technical) troubleshooting from the mechanic. Thanks for sharing.

In summary- It's either the throttle body motor or the vehicle's ECM causing the fault. In the case of the Lexus in video, it was a bad ECM.

Bummer.

 

The throttle motor is operated by a PWM (Pulse Width Modulation) signal from the ECM so you cannot really measure the voltage there. An oscilloscope could measure/display this signal.

When everything is good, you would hear a humming sound from the throttle body at ignition "on" (engine not started) and the throttle plate would open a little bit. If you don't hear the humming, you can first test the throttle motor by connecting an ohmmeter (ohm range) to the two pins in the motor side of the round pin. It should read about 23 ohm (taken from my new TB, AJ26 but AJ27 should be similar).

If you get the mentioned ohm reading, you can then test whether the throttle motor is actually working if you connect 12V supply to the two motor wires but with a 5W bulb in series. The bulb should light dim and the throttle plate may move. If the plate does not move, change the polarity of the 12V supply. The plate may not move with either orientation of the supply (due to limited current by the bulb) but you should hear some clicking from the TB. If the bulb does not light at all, the throttle motor is bad.

 

SOLVED!

I'm embarrassed to admit my solution, but I owe it to anyone else that's as dumb as me and might stumble across this post in the future...

When doing my smoke testing for an EVAP leak, I plugged up one of the air intake ports with a rag. Well, because the rag was pushed far enough in to be hidden, I completely missed it during my reassembly. When I popped off the intake to start the TB removal, there was the forgotten rag lodged sitting on top of the butterfly valve.

With the intake and TB clear, we're back up an running without issue.