Fix P20B8: STEP-BY-STEP diagnostic GUIDE!

The P20B8: Reductant Metering Unit Heater Control Circuit High refers to a condition where the voltage in the control circuit for the metering unit heater is higher than expected. This could indicate an electrical problem, such as excessive voltage supply to the heater, or issues with the control module or the heater itself.

P20B8 – Quick Overview

CodeInformation
MeaningP20B8: Reductant Metering Unit Heater Control Circuit High
Is it serious?Yes, this issue can cause improper functioning of the reductant system, leading to increased emissions or heater failure.
Possible causes– High voltage in the metering unit heater control circuit
– Faulty heater
– Faulty control module
How to diagnose?– Measure voltage in the heater control circuit
– Test the metering unit heater
– Check the control module functionality

P20B8 Meaning

The P20B8 fault code indicates that the voltage in the control circuit of the reductant metering unit heater is too high, which can negatively impact the performance of the heater. This may result from electrical issues in the circuit, such as excess voltage being supplied, or due to a fault in the heater or control module.

Step-by-step diagnostic guide

ActionDescriptionTools Needed
Check for Other CodesUse an OBD-II scanner to check for any other codes that might provide more information about the issue.OBD-II Scanner
Measure Voltage in the Heater Control CircuitMeasure the voltage in the metering unit heater control circuit using a multimeter. Ensure the voltage is within the manufacturer-specified range.Multimeter
Test the Metering Unit HeaterUse a diagnostic tool to test the heater’s functionality and confirm that it is working correctly and not receiving too much power.Multimeter, Diagnostic Tool
Inspect the Control ModuleVerify the control module to ensure it is functioning correctly and not causing an excessive voltage supply.Diagnostic Tool
Repair or Replace Wiring/HeaterIf the voltage is too high, inspect the wiring for faults, and repair or replace the heater if necessary.Wiring Kit, Replacement Heater
Clear the Code and Test DriveAfter performing repairs, clear the code with an OBD-II scanner and test drive the vehicle to confirm the problem is resolved.OBD-II Scanner, Vehicle Manual
Recheck for CodesAfter the test drive, rescan the vehicle to ensure the P20B8 code does not return.OBD-II Scanner
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