AutoCodes – RAM – P20B8 RAM

P20B8 RAM Code - Diesel Exhaust Fluid Reductant Pump Heater Control Circuit High

Quick Answer

The Powertrain Control Module (PCM) controls the Diesel Exhaust Fluid (DEF) Heaters via datalink communication with the Diesel Exhaust Fluid Dosing Control Unit (DEF DCU - sometimes referred to as the Selective Catalytic Reduction (SCR) Module). Common causes include Selective Catalytic Reduction (SCR) Module Circuit, Faulty DEF Supply Pump Assembly, Faulty Diesel Exhaust Fluid Dosing Control Unit (DEF DCU). Severity is High - diagnose this code as soon as possible. Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.

What it means: P20B8 RAM indicates Diesel Exhaust Fluid Reductant Pump Heater Control Circuit High.
Common causes: Common causes include Selective Catalytic Reduction (SCR) Module Circuit, Faulty DEF Supply Pump Assembly, Faulty Diesel Exhaust Fluid Dosing Control Unit (DEF DCU).
Severity: High - diagnose this code as soon as possible.
Can I drive?: Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.

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Code Popularity 243

How popular is this code, among other codes? Low

Repair Importance Level

Urgent (Diagnose now) (3 / 3)

Repair Difficulty Level

Advanced (Pro) (3 / 3)

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Table of contents Created and updated by William Orellana on Oct 13, 2023

Description
Possible Causes
How To Fix
Cost to Diagnose
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Code P20B8 RAM Description

The Powertrain Control Module (PCM) controls the Diesel Exhaust Fluid (DEF) Heaters via datalink communication with the Diesel Exhaust Fluid Dosing Control Unit (DEF DCU - sometimes referred to as the Selective Catalytic Reduction (SCR) Module). The DEF DCU receives two voltage supplies: One from the SCR Relay 1 (which is activated upon startup). And the other is a fused B+ supply. The DEF Tank electric heater and DEF Line Heater power supply and ground circuits are wired directly to the DCU. The DEF Tank Heater is integrated into the DEF Supply Pump assembly and is not serviced separately.
Activation of the DEF Supply Line and DEF Tank Heaters operate independently of each other. Line heating is based on the Ambient Temperature Sensor input and Tank heating is based on the DEF Tank Temperature Sensor value. Heating of the Line or Tank Heater is initiated when the corresponding temperature value is below -5°C (23°F). Heating stops when the corresponding temperature value goes above -4°C (24.8°F). The DEF Dosing Control Unit monitors these inputs and reports them to the Powertrain Control Module (PCM). The PCM will illuminate the MIL lamp after this diagnostic runs and fails. The PCM will turn off the MIL light when the monitor runs and passes in three consecutive key cycles. The Diagnostic Trouble Code (DTC) will be set when the DEF Dosing Control Unit detects that the SCR Module Heater Supply circuit voltage is above a calibrated value.

OBDII Code P20B8 RAM - Diesel Exhaust Fluid Reductant Pump Heater Control Circuit High - AutoCodes.com — P20B8 RAM Code - Diesel Exhaust Fluid Reductant Pump Heater Control Circuit High

What does this mean?

What are the Possible Causes of the DTC P20B8 RAM?

Selective Catalytic Reduction (SCR) Module Circuit
Faulty DEF Supply Pump Assembly
Faulty Diesel Exhaust Fluid Dosing Control Unit (DEF DCU)
Faulty Power Distribution Center

How to Fix the DTC P20B8 RAM?

Review the 'Possible Causes' above and visually examine the corresponding wiring harness and connectors. Check for damaged components and inspect connector pins for signs of being broken, bent, pushed out, or corroded.

What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the P20B8 RAM code, it typically requires 1.0 hour of labor. Rates vary by location, vehicle, and shop. Many shops charge between $80–$150 per hour; dealerships and metro areas may be higher, independents may be lower.

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About the author: William Orellana is a Master Mechanic and Mechanical Engineer with over 30 years of experience diagnosing and repairing vehicles. Learn more about his background.