Clunky engine, stalling, no acceleration, p2103

DTC P2103 means that the engine control module (ECM) thinks that the throttle body motor is drawing excessive current, more than 10A. So the ECM sets the throttle plate opening to a fixed opening (16 degrees) and puts the car in limp home mode.

1. Disconnect the throttle motor wiring harness connector and measure resistance across the terminals of the motor. The spec at 68 degrees F is 0.3 ohm to 100 ohms, which seems like a pretty big range. In case it is not obvious, you need to account for the resistance of the meter leads by first shorting the test leads together and noting the digital multimeter reading. Suppose the reading is 0.3 ohm. Then subtract that value from whatever subsequent resistance measurements you take.

2. If the motor resistance is within spec, then measure resistance of the wiring harness connector to body ground. At either terminal the resistance to ground should be more than 10K ohms.

3. Finally, measure resistance from each terminal of the wiring harness connector to the appropriate ECM wiring harness connector. At this point I am going to refer you to techinfo.toyota.com so that you can obtain the factory repair manual info, can see the illustrations, etc.

4. Since the engine is producing inadequate power, it is certainly possible that has provoked the high voltage traction battery to fail. Considering the odometer reading on your car, such a failure is way past due.

 

What are you using to scan the codes? A generic OBD reader might not be able to read all the codes. You say the throttle plate moves ok but since it opens and closes electrically if that part is bad moving the throttle plate would not show that.

 

At those prices it made good sense to buy both. That also shows you those parts have a low failure rate since the demand apparently is low. I suggest you use a new throttle body gasket to ensure no vacuum leaks downstream from the mass air flow sensor.

Since you have a new throttle body on the way, maybe it would be fun to apply voltage to the original throttle motor and see what happens. Just apply voltage momentarily so you can assess the motor behavior.

The ECM probably applies a pulse modulated waveform to control the throttle opening

 

Since you had measured 4.1 ohms resistance at the motor, that implies the motor will draw 3A current when 12V is applied. (current x resistance = voltage per Ohm's Law) That amount of current flow would create some sparking.

While you are waiting for the new throttle body to arrive, maybe you might reinstall the old one now that you've fully exercised it by applying battery power, and see if there is any difference. Just if you need some fun over the weekend.

 

Congrats on your success!

An alternative to losing the coolant would be to plug the hoses. I bought a bunch of soft silicone rubber plugs in various sizes for that purpose. A makeshift alternative would be to use a couple of pencil stubs, or some such thing.

 

Hoping it would help someone in the future, I would like to share my experience on this topic:
2005 (Gen 2) Prius: we first encountered this issue last December: P2103, I cleaned the TB with TB cleaner, then P2111. Also, the Red triangle, and "HV Battery" message on the display came up, after the HV battery was almost depleted when the electric motor tried to compensate for the very poor idling of the petrol engine.
I waited 2 days, replaced the Throttle Body - and that fixed everything. Before starting the engine with the new TB, I waited 2 days, also removed the 12V battery for a while, so the HV SoC was reset: the card started this way "believing" that the SoC was 3 bars instead of 0 (that I saw before, when I was the red triangle).

No problems for 3 months, then the car completely stopped (my wife drove it, she could pull to the side luckily). I checked the codes: P2103 again. I didn't wan to just buy another Throttle Body, so I checked my old TB (that I removed 3 months ago): the problem was that the Throttle Position Sensor was stuck in this position:



It has its own, small spring that is supposed to bring the TPS back to it's starting position:



So the big spring of the TB only returns the TB to the starting position, but not the TPS! That small TPS spring was dry, but quite dusty. Also: there was a very small plastic molding error in the TPS inner housing that made this small spring's life harder: I think mostly that caused this stuck. I cleaned the spring with alcohol (it moved much better after cleaning) and with a small knife, I cut (actually filed) this very small plastic molding error.

But: officially the TPS is not a replaceable part for Priuses (at least for Gen2). So the official method it to replace the Throttle Body. But the exact same TPS is a replaceable part for some other Toyotas, so I started checking it. In the factory, the TPS screws on the TB are marked with a yellow paint. You can try to just use the paint marks to place the TPS back to it's good position, but a better method is to measure the correct value:

In the Prius documentation the VTA1 and VTA2 voltage ranges are specified for the TPS. Since the ECM is using 5V for the TPS, I used a stabilized 5V source to measure the voltages. I set the screws so the VTA1 was 0.7V and VTA2 was 2.3V.

The VTA ranges are quite large BTW:
Throttle position sensor VTA1 voltage: 0.6 to 3.96 V
Throttle position sensor VTA2 voltage: 2.25 to 5.0 V

To assist anyone in the future, I measured the resistance of this setup:
- between the Red and Pink contacts: 1682 Ohms
- between the Red and Blue contacts: 1243 Ohms

It was in March, car is perfect since then. I hope it will be useful for someone! Also, thanks for all the above, and other related posts here, as it really helped me back then!