Prius Gen 2 – P2103 after washing, engine won’t start, hybrid battery drains fast

Hi everyone,

I’m having a recurring issue with my 2006 Toyota Prius Gen 2 and I’m hoping someone here has seen this before.

Problem:
After washing the car with a pressure washer, I get a Check Engine light and code P2103 (Throttle Actuator Control Motor Circuit High).

At the same time:

• The engine will not start
• The hybrid battery drains very quickly (within seconds)
• Multiple warning lights appear
• Eventually the car won’t start at all

It seems like the hybrid system is trying to run, but the engine never kicks in.

History:
This has happened 3 times so far:

• The first two times, I left the car parked for 3–4 days
• After that, it started normally again
• Check Engine light stayed on briefly, then disappeared
• Car ran perfectly afterward

Current situation:
This time, the engine no longer starts even after waiting.

What I’ve tried:

• Replaced the throttle body twice (no change)
• Same P2103 code returns

Observations:

• Issue only appears after pressure washing
• Seems strongly related to moisture
• Temporary recovery in the past suggests something dries out and starts working again

Questions:

• Could this be a wiring harness issue?
• Are there known weak points for water intrusion on Gen 2 Prius?
• Could it be a bad ground or ECU connector?
• Where should I focus diagnostics next?

Any advice or similar experiences would be greatly appreciated.

Thanks!

 

I finally found the cause of the problem: damaged wiring that was creating an intermittent short circuit.
*Note for those asking about the washing: I was washing the exterior of the car only using a normal pressure jet wash.

Initially, I tested the wiring between the ECM and the throttle body (checking for continuity and ground), and everything seemed fine, so I ruled it out. However, it turns out the issue was still in the wiring — it was creating a short only under certain conditions.

The damage was most likely caused by a mouse/rat. Several wires and nearby hoses in the engine bay had their insulation chewed. At first, I wasn’t sure if it was rodent damage or just aging insulation, but it became clear it was from an animal.

When I washed the car, water would drip onto the exposed wires and cause a short circuit. This explains why:

• the errors appeared after washing
• the car sometimes worked again after a few days (once everything dried out)

In the end, an auto electrician repaired the damaged wiring and insulation, and the problem is now completely gone

Hopefully this helps someone else — if you have similar symptoms, definitely check your wiring carefully, even if initial tests seem OK.


Many thanks to @bisco @ChapmanF @PriusCamper for your support!