P20B4 — Reductant Heater Coolant Control Valve Circuit High

What Does P20B4 Mean?

P20B4 is a diagnostic trouble code indicating: Reductant Heater Coolant Control Valve Circuit High. This code relates to the powertrain system. The vehicle's computer detected a condition outside normal operating parameters and stored this code.

Symptoms of P20B4

⚠️ Check Engine Light (MIL) illuminated
⚠️ Reductant Heater Coolant Control Valve reading stuck at maximum value
⚠️ Related system operating erratically or in default mode
⚠️ Reduced engine performance

Common Causes

🔍 Short to voltage in Reductant Heater Coolant Control Valve wiring harness
🔍 Corroded or water-damaged Reductant Heater Coolant Control Valve connector
🔍 Faulty Reductant Heater Coolant Control Valve outputting maximum voltage
🔍 Damaged wiring rubbing against metal components
🔍 ECM/PCM internal fault (rare)

Frequently Asked Questions

What does P20B4 mean?

P20B4 indicates: Reductant Heater Coolant Control Valve Circuit High. The vehicle's computer has detected that the Reductant Heater Coolant Control Valve is not operating within its expected parameters and stored this diagnostic trouble code.

Can I drive with code P20B4?

You can drive short distances for essential trips, but schedule a diagnosis soon. Driving with P20B4 for extended periods may cause additional problems.

How much does it cost to fix P20B4?

Repair costs for P20B4 typically range from $20 to $300, depending on the root cause. Simple wiring or connector repairs are on the lower end, while component replacement costs more. A proper diagnosis ($80–$150 at most shops) will identify the exact cause before committing to expensive parts.

What To Do Next

Possible Fixes

🔧 Inspect and repair Reductant Heater Coolant Control Valve wiring for short to voltage
🔧 Clean or replace corroded Reductant Heater Coolant Control Valve connector
🔧 Replace faulty Reductant Heater Coolant Control Valve

1
Find your vehicle above
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2
Check for recalls
Go to nhtsa.gov/recalls and enter your VIN. Free repairs if covered.
3
Get a professional diagnosis
A code alone doesn't identify the exact failed part. A diagnostic ($50–$150) pinpoints the root cause.

P20B4: Reductant Heater Coolant Control Valve Circuit High