P21B1 — Reductant Level Sensor C Circuit Intermittent/Erratic

What Does P21B1 Mean?

P21B1 is a diagnostic trouble code indicating: Reductant Level Sensor C Circuit Intermittent/Erratic. This code relates to the powertrain system. The vehicle's computer detected a condition outside normal operating parameters and stored this code.

Symptoms of P21B1

⚠️ Check Engine Light (MIL) illuminated
⚠️ Reductant Level Sensor C signal cutting in and out
⚠️ Related system working sometimes but not consistently
⚠️ Reduced engine performance

Common Causes

🔍 Loose or intermittent connection at Reductant Level Sensor C
🔍 Wire chafing causing intermittent contact
🔍 Reductant Level Sensor C failing under heat or vibration
🔍 Corroded connector pins with partial contact

Frequently Asked Questions

What does P21B1 mean?

P21B1 indicates: Reductant Level Sensor C Circuit Intermittent/Erratic. The vehicle's computer has detected that the Reductant Level Sensor C is not operating within its expected parameters and stored this diagnostic trouble code.

Can I drive with code P21B1?

Yes, P21B1 is generally safe to drive with in the short term. However, it should still be addressed to pass emissions testing and prevent potential secondary issues.

How much does it cost to fix P21B1?

Repair costs for P21B1 typically range from $30 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 reseat all Reductant Level Sensor C connectors
🔧 Repair chafed or damaged wiring in Reductant Level Sensor C circuit
🔧 Replace Reductant Level Sensor C if failing intermittently

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.

P21B1: Reductant Level Sensor C Circuit Intermittent/Erratic