U02A4 — Lost Communication With NH3 Sensor

What Does U02A4 Mean?

U02A4 is a diagnostic trouble code indicating: Lost Communication With NH3 Sensor. This code relates to the manufacturer-specific network system. The vehicle's computer detected a condition outside normal operating parameters and stored this code.

Symptoms of U02A4

⚠️ Check Engine Light (MIL) illuminated
⚠️ No communication with NH3 Sensor
⚠️ Multiple warning lights may illuminate simultaneously
⚠️ Related system completely inoperative
⚠️ Multiple warning lights on dashboard

Common Causes

🔍 CAN bus wiring fault (open or shorted) to NH3 Sensor
🔍 Power or ground supply issue to NH3 Sensor
🔍 NH3 Sensor internal failure
🔍 Water intrusion damaging module or connectors
🔍 CAN bus termination resistor fault

Frequently Asked Questions

What does U02A4 mean?

U02A4 indicates: Lost Communication With NH3 Sensor. The vehicle's computer has detected that the NH3 Sensor is not operating within its expected parameters and stored this diagnostic trouble code.

Can I drive with code U02A4?

You can drive short distances for essential trips, but schedule a diagnosis soon. Driving with U02A4 for extended periods may cause additional problems.

How much does it cost to fix U02A4?

Repair costs for U02A4 typically range from $80 to $1200, 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 CAN bus wiring to NH3 Sensor for damage
🔧 Check power and ground supply to NH3 Sensor
🔧 Replace failed NH3 Sensor

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.

U02A4: Lost Communication With NH3 Sensor