What Does P202B Mean?
The DEF tank heater control circuit voltage is lower than expected. This indicates a short to ground, excessive current draw, or control circuit fault in the reductant heating system.
Common Causes
40%
Short to ground in DEF heater wiring harness
30%
Failed DEF tank heater with internal short
15%
Damaged or corroded heater connector causing short
10%
Failed control module output driver circuit
5%
Chafed wiring due to improper routing or installation
Diagnostic Steps
1
Step 1: Disconnect DEF tank heater connector and measure resistance to ground on heater side (should be very high resistance/open)
2
Step 2: Check wiring harness for shorts to ground using multimeter with heater disconnected
3
Step 3: Inspect wiring routing for areas where harness may contact chassis or hot components
4
Step 4: Measure heater element resistance and compare to specifications
5
Step 5: Test control module output circuit with heater disconnected for proper voltage and current capability
Estimated Repair Cost
$150 - $900
Parts + labor, varies by vehicle and location
The DEF tank heater control circuit voltage is lower than expected. This indicates a short to ground, excessive current draw, or control circuit fault in the reductant heating system.
The most common cause of P202B (Reductant Tank Heater Control Circuit Low) is: Short to ground in DEF heater wiring harness
Typical repair costs for P202B range from $150 to $900, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Safe to drive temporarily. Prolonged operation may result in frozen DEF in cold climates and eventual engine derate to protect emissions system.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P202B to identify the root cause.
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Quick Info
Category
Powertrain
System
Selective Catalytic Reduction (SCR) Emissions System
Difficulty
Type
Generic (SAE)
Recommended Tools
OBD2 Scanner
A quality scan tool helps you read codes, view live data, and clear faults.
