P0ADC🔧 Hybrid system (high-voltage battery relays)Stop and fix promptly

P0ADC: Hybrid Battery Positive Contactor Control Circuit High (Meaning, Causes, Fixes)

Reviewed 2026-10-24 · Based on 3 cited source(s)

What P0ADC means

A hybrid's high-voltage battery is connected and disconnected by heavy-duty relays that Toyota calls system main relays (SMRs) and the generic code list calls contactors. Toyota's 2008 Prius service manual explains that there are three: one on the negative side and two on the positive side. When the car starts, SMR1 and SMR3 close first, so current flows through a resistor and the circuit is protected from a surge; then SMR2 closes and SMR1 opens. The hybrid (HV) control computer watches each relay, and P0ADC with Toyota information code 226 means it found a fault in the No. 2 system main relay (CON2) circuit. Toyota's 2004 Prius manual lists the same information code 226 under an older code number, P0AA1, and gives the detection condition as an open or a short to battery voltage (+B) in the No. 2 system main relay circuit. RepairPal describes P0ADC more generally: the hybrid control module engages and disengages the high-voltage system, and the code sets if that module cannot control the circuit to the high-voltage battery. The companion code P0ADB means the same circuit reads low.

Severity: can I keep driving?

Stop and fix promptly

Get it checked soon. RepairPal rates P0ADC as Urgent and says the hybrid control module may shut down the high-voltage system, so the car may not run on its hybrid system or charge its battery. This is a high-voltage circuit, so the fix is a job for a trained hybrid technician. The check engine light will also fail an emissions inspection.

Common symptoms

Likely causes

Roughly most to least common, based on the sources below. Your vehicle may differ.

  1. A faulty No. 2 system main relay, the positive-side contactor (Toyota Prius manuals)
  2. An open or short in the wiring or connectors between the hybrid control computer and that relay (Toyota Prius manuals; RepairPal lists a wiring issue)
  3. A failed hybrid control computer (Toyota Prius manuals; RepairPal lists high-voltage control module failure)
  4. A weak or failing 12-volt auxiliary battery (RepairPal)

Diagnostic steps you can do

⚠ Before you start

Work on a cool engine, parked on level ground with the parking brake set. Never work under a car supported only by a jack.

  1. Safety first: the relays this code is about switch the high-voltage battery, which can kill. Toyota's manual says to wear insulated gloves, remove the service plug and keep it in your pocket, and wait at least 5 minutes for the inverter's capacitor to discharge before touching any high-voltage part. Don't open the battery or relay area yourself.
  2. Read every stored code with a scan tool and write them down, including any Toyota information code (such as 226) if your tool shows it.
  3. Test or charge the 12-volt auxiliary battery and make sure its terminals are clean and tight, since RepairPal lists a failing 12-volt battery as a cause.
  4. Check for recalls and service bulletins for your car before paying for parts.

Typical fixes

Repair costs vary widely by vehicle, region, parts brand and shop, so we don't quote prices. Get a written estimate after diagnosis.

🛠 When to call a pro

  • Any work on the high-voltage battery, its relays or orange high-voltage cables
  • The car won't go into Ready or drive
  • Testing the relay and harness needs the service plug removed and insulated gloves, which is hybrid-technician work
  • Ask a dealer whether hybrid-system warranty coverage applies before paying for a relay or control computer

Where to buy

Plain search links. Always match parts to your exact year, make, model and engine.

OBD2 scanners on Amazon Parts at Advance Auto Parts catalog at RockAuto

FAQs

Is P0ADC serious?

Yes. RepairPal rates it Urgent and says the hybrid control module may disable the high-voltage system, so the car may not run on its hybrid system or charge. Have it diagnosed soon by a shop that works on hybrids.

What is a hybrid battery positive contactor?

It's a heavy-duty relay that connects the positive side of the high-voltage battery to the rest of the hybrid system. Toyota calls these system main relays; its Prius manual says there are two on the positive side and one on the negative side, and P0ADC (information code 226) points to the No. 2 relay.

Do the sources agree on P0ADC?

Mostly. Toyota's manuals point to the No. 2 system main relay, its wiring, or the hybrid control computer. RepairPal describes the code more generally as the hybrid control module being unable to control the circuit to the high-voltage battery, and it also lists a failing 12-volt battery, which Toyota's procedure for this code doesn't mention. Toyota's own numbering also changed: the 2004 Prius manual lists the same fault (information code 226) as P0AA1, while the 2008 manual calls it P0ADC-226.

How much does it cost to fix P0ADC?

None of the sources give a repair cost. The fix can be a 12-volt battery, a wiring repair, a relay or the hybrid control computer, so get a proper diagnosis before buying parts.

Sources

  1. RepairPal: P0ADC Hybrid Battery Positive Contactor Control Circuit High (rated Urgent)
  2. Toyota 2008 Prius service manual: DTC P0ADC-226 Hybrid Battery Positive Contactor Control Circuit High (hosted copy on LEMON Manuals)
  3. Toyota 2004 Prius repair manual (RM1075U), DTC P0AA1/226 and P0AA2/227: system main relay No. 2 circuit (hosted PDF copy)

Last reviewed 2026-10-24. Code definitions and repair steps can vary by manufacturer. Confirm with your vehicle's service information.