P21CA: Reductant Control Module Supply Voltage Circuit

Severity

Medium

System

Powertrain

Last reviewed: Jan 1, 0001 Last updated: Jan 1, 0001

Methodology: We combine code standards with complaint and reliability patterns, then review for clear, vehicle-first diagnosis steps.

Sources: SAE/OBD-II definitions, manufacturer service information, and public reliability reports (including NHTSA where applicable).

Limits: Guidance is informational and may not match every model-year or revision. Confirm with the official manual and diagnostics before replacing parts. For safety-critical or electrical work, use a qualified technician.

What Does P21CA Mean?

P21CA is a diagnostic trouble code indicating: Reductant Control Module Supply Voltage Circuit. This code relates to the powertrain system. The vehicle's computer detected a condition outside normal operating parameters and stored this code.

Symptoms of P21CA

⚠️ Check Engine Light (MIL) illuminated
⚠️ Erratic Reductant Control Module Supply Voltage readings
⚠️ Related system operating intermittently
⚠️ Reduced engine performance

Common Causes

🔍 Wiring issue in Reductant Control Module Supply Voltage circuit (damaged, chafed, or corroded)
🔍 Faulty Reductant Control Module Supply Voltage connector or terminal
🔍 Failed Reductant Control Module Supply Voltage
🔍 ECM/PCM connection issue

Frequently Asked Questions

What does P21CA mean?

P21CA indicates: Reductant Control Module Supply Voltage Circuit. The vehicle's computer has detected that the Reductant Control Module Supply Voltage is not operating within its expected parameters and stored this diagnostic trouble code.

Can I drive with code P21CA?

You can drive short distances for essential trips, but schedule a diagnosis soon. Driving with P21CA for extended periods may cause additional problems.

How much does it cost to fix P21CA?

Repair costs for P21CA typically range from $80 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 Control Module Supply Voltage wiring and connectors
🔧 Replace faulty Reductant Control Module Supply Voltage

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.