Reductant Level Sensor Circuit Low
The P203C code indicates that the reductant (DEF) level sensor circuit is reading a voltage lower than the expected range. This sensor monitors the fluid level in the DEF tank for the selective catalytic reduction (SCR) system. A low circuit condition typically means the sensor signal is shorted to ground or the sensor itself has failed, causing the PCM to detect an implausibly low voltage. This can lead to incorrect DEF level readings, potentially triggering warning lights and reducing engine performance to protect the emissions system.
01. Most Common Causes
- Faulty reductant level sensor
- Short to ground in sensor wiring or connector
- Corroded or damaged sensor connector
- Open circuit in sensor signal wire
- Failed PCM (rare)
02. Symptoms You Will Notice
- Check Engine Light illuminated
- DEF level warning light or message on dashboard
- Reduced engine power or limp mode
- Possible inability to start after extended idling
- Increased emissions due to improper DEF dosing
03. Step-by-Step Diagnosis
Step 1: Use a scan tool to confirm P203C and check for related codes (e.g., P203D, P203E).
Step 2: Visually inspect the DEF level sensor connector and wiring for damage, corrosion, or shorts.
Step 3: Measure voltage at the sensor signal wire with key on; should be 0.5-4.5V depending on fluid level. If near 0V, suspect short to ground.
Step 4: Disconnect sensor and check resistance between signal and ground; infinite resistance indicates open, low resistance indicates short.
Step 5: If wiring and connector are good, replace the reductant level sensor.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive long distances with this code. The vehicle may enter limp mode to protect the SCR system, and continued driving could cause further emissions system damage or lead to a no-start condition.
How much does it cost to fix?▼
The cost to fix P203C typically ranges from $50 to $150 for parts and labor, depending on the vehicle and whether the sensor or wiring needs replacement. The sensor itself is usually $30-$80, and labor is about $20-$70.