P20B8 — Reductant Metering Unit Heater Control Circuit High

What Does P20B8 Mean?

P20B8 is a diagnostic trouble code indicating: Reductant Metering Unit Heater Control 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 P20B8

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

Common Causes

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

Frequently Asked Questions

What does P20B8 mean?

P20B8 indicates: Reductant Metering Unit Heater Control Circuit High. The vehicle's computer has detected that the Reductant Metering Unit Heater is not operating within its expected parameters and stored this diagnostic trouble code.

Can I drive with code P20B8?

You can drive short distances for essential trips, but schedule a diagnosis soon. Driving with P20B8 for extended periods may cause additional problems.

How much does it cost to fix P20B8?

Repair costs for P20B8 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 Metering Unit Heater wiring for short to voltage
🔧 Clean or replace corroded Reductant Metering Unit Heater connector
🔧 Replace faulty Reductant Metering Unit Heater

1
Find your vehicle above
Click your make and model for real owner reports and common causes specific to your vehicle.
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.

P20B8: Reductant Metering Unit Heater Control Circuit High