✅ P003400 – Turbocharger Bypass Valve Control Circuit Low

Meaning:

The ECU is seeing lower-than-expected voltage in the control circuit of the turbo bypass valve / diverter valve / wastegate bypass valve.

This usually points to an electrical issue, not a mechanical one.

✅ Common Causes

Electrical (Most common):

1. Open circuit in the bypass valve connector or wiring

2. Short to ground in the control wire

3. Corroded / loose connector pins

4. Faulty bypass valve solenoid

5. Faulty power supply (low voltage)

6. ECU driver failure (rare)

Mechanical

Bypass valve stuck open/closed (less common for this code)

🔧 Step-by-Step Diagnosis for Your Workshop

1️⃣ Inspect the Turbo Bypass Valve & Connector

Locate the bypass valve (usually near turbo compressor housing).

Check:

✔ Broken wires

✔ Oil contamination inside connector

✔ Loose pins

✔ Corrosion

If found → repair and clear code.

2️⃣ Check Power Supply to the Valve

Most bypass valves work on 12V supply + ECU-controlled ground.

With ignition ON:

Pin 1 (usually) → Should have battery voltage (12V)

Pin 2 (control) → ECU ground pulse

If no 12V supply → trace back to fuse/relay/power distribution.

3️⃣ Check Resistance of the Bypass Valve Solenoid

Disconnect valve and measure:

Normal range: 20–40 ohms (varies by manufacturer)

If reading is:

Open circuit (∞ ohm) → Solenoid failed

Very low resistance (<5 ohms) → Shorted solenoid

→ Replace valve.

4️⃣ Check Control Circuit (from ECU)

Use a test light or multimeter:

Connect test light between control wire and battery positive

Start engine →

Test light should flicker, showing ECU pulsing the valve.

If no pulse:

Wire is open/short

ECU driver possibly faulty

5️⃣ Check Turbo Boost Operation

If the valve is stuck open, you will see:

Low boost

Slow acceleration

Turbo sound abnormal

(This code alone usually indicates electrical, not mechanical.)

🛠️ Common Fixes in Real Workshops

Repair damaged wiring near turbo (heat damage is common)

Clean and refit corroded connectors

Replace bypass valve solenoid

Restore power supply from fuse/relay

Reflash/update ECU (for some Hyundai/Kia/VW engines)

Rare: Replace ECU

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