P20BB – Reductant Heater Control Circuit High

P20BB: Reductant Heater 'A' Control Circuit Low

The P20BB diagnostic trouble code (DTC) indicates that the powertrain control module (PCM) has detected insufficient voltage in the control circuit for the on-board reductant heater 'A'. This code is primarily associated with diesel engines equipped with selective catalytic reduction (SCR) systems.

Urgency and Drivability

While P20BB is not immediately critical, it should be addressed promptly. You can typically continue driving, but prolonged operation may lead to:

1. Reduced SCR system efficiency
2. Potential damage to the catalytic converter
3. Decreased fuel economy
4. Possible entry into limp mode in severe cases

It's advisable to have the issue diagnosed and repaired within 100-200 miles (160-320 km) of the code appearing.

Code Specifics

P20BB is a generic powertrain code applicable to many OBD-II vehicles manufactured from 1996 onwards, including Ford, Mercedes-Benz, Audi, RAM, Chevrolet, BMW, and GMC. While the basic definition remains consistent across manufacturers, specific diagnostic procedures and repair steps may vary.

Components Involved

1. Reductant Heater: Typically located inside the diesel exhaust fluid (DEF) tank
2. PCM: Monitors and controls the reductant heater circuit
3. Wiring harness and connectors
4. Fuses and relays in the reductant heater circuit

The reductant heater's primary role is to warm the DEF, preventing crystallization in cold temperatures and ensuring proper SCR system function.

Common Causes

1. Damaged or corroded wiring in the reductant heater circuit
2. Faulty reductant heater
3. Failed PCM or glow plug control module
4. Blown fuses or damaged relays
5. Contaminated or degraded DEF

Diagnostic Procedure

1. Connect an OBD-II scanner and retrieve all stored codes and freeze frame data.
2. Visually inspect the reductant heater system harnesses and connectors for damage or corrosion.
3. Check and test related fuses and relays.
4. Use a digital multimeter to test the power supply to the SCR control system:
   • Battery voltage should be present at the power supply circuit
   • Ground circuit should show less than 0.1 ohms resistance to chassis ground
5. Activate the reductant heater using a scan tool and measure the output control circuit voltage.
6. Test the reductant heater element resistance:
   • Typical resistance range: 0.5 – 2.0 ohms at 20°C (68°F)
   • Exact specifications vary by manufacturer
7. Check for related TSBs (Technical Service Bulletins) specific to the vehicle make and model.

Solutions

1. Repair or replace damaged wiring and connectors
2. Replace faulty reductant heater
3. Update PCM software if available
4. Replace blown fuses or damaged relays
5. In severe cases, replace the PCM or glow plug control module

Prevention

1. Regular inspection of the DEF system and related components
2. Use high-quality DEF and maintain proper fluid levels
3. Address any DEF-related warning lights promptly
4. Perform scheduled maintenance as per manufacturer recommendations

Repair Costs

• Diagnostic fee: $75 – $150 (€65 – €130)
• Reductant heater replacement: $200 – $500 (€175 – €435)
• Wiring repair: $100 – $300 (€85 – €260)
• PCM replacement (if necessary): $500 – $2000 (€435 – €1740)

Parts costs can vary significantly based on vehicle make and model. Labor rates typically range from $75 to $150 (€65 – €130) per hour.

Related Issues and Fault Codes

P20BB often occurs in conjunction with other DEF and SCR system-related codes:

1. P20B9: Reductant Heater 'A' Control Circuit Open
2. P20BA: Reductant Heater 'A' Control Circuit High
3. P20BC: Reductant Heater 'B' Control Circuit Low
4. P208E: Reductant Pump Control Circuit Low
5. P203B: Reductant Level Sensor Circuit Low

These codes may indicate broader issues within the SCR system and should be diagnosed comprehensively.

By addressing P20BB promptly and maintaining your vehicle's DEF system, you can ensure optimal performance and longevity of your diesel engine's emissions control systems.

Frequently Asked Questions About P20BB

What does the P20BB code mean?

P20BB indicates a “Reductant Heater ‘A’ Control Circuit Low” condition, meaning the powertrain control module (PCM) has detected insufficient voltage in the control circuit for the on-board reductant heater ‘A’.

Which vehicles commonly experience the P20BB code?

This code is common in diesel vehicles with selective catalytic reduction (SCR) systems, including makes like Ford, Mercedes-Benz, Audi, RAM, Chevrolet, BMW, and GMC.

Is it safe to drive with the P20BB code?

While not immediately critical, it’s advisable to address the issue promptly. Continued driving may lead to reduced SCR efficiency, potential catalytic converter damage, and decreased fuel economy.

What are the main symptoms of the P20BB code?

Common symptoms include reduced engine performance, excessive black exhaust smoke, decreased fuel efficiency, and illumination of the check engine light.

What causes the P20BB code to appear?

Common causes include damaged wiring, a faulty reductant heater, failed PCM, blown fuses, damaged relays, or contaminated diesel exhaust fluid (DEF).

How is the P20BB code diagnosed?

Diagnosis typically involves using an OBD-II scanner, visually inspecting wiring and connectors, testing fuses and relays, and measuring voltage and resistance in the reductant heater circuit.

Can I diagnose and fix the P20BB code myself?

While some diagnostic steps can be performed by experienced DIYers, professional diagnosis is recommended due to the complexity of SCR systems.

How much does it cost to repair the issue causing the P20BB code?

Repair costs can vary widely, from $100 for simple wiring repairs to $2000 or more for PCM replacement, not including diagnostic fees.

What components are involved in the P20BB code?

Key components include the reductant heater, PCM, wiring harness, connectors, fuses, and relays in the reductant heater circuit.

How does the reductant heater function in the SCR system?

The reductant heater warms the diesel exhaust fluid (DEF) to prevent crystallization in cold temperatures, ensuring proper SCR system function.

Are there any related codes that often appear with P20BB?

Yes, related codes include P20B9, P20BA, P20BC, P208E, and P203B, which are all associated with the DEF and SCR systems.

How can I prevent the P20BB code from occurring?

Regular maintenance, using high-quality DEF, maintaining proper fluid levels, and promptly addressing DEF-related warning lights can help prevent this issue.

Will the P20BB code clear itself?

While the code may clear itself if the issue resolves temporarily, it’s unlikely to stay cleared without addressing the underlying problem.

How does the P20BB code affect vehicle emissions?

This code can lead to reduced SCR system efficiency, potentially causing the vehicle to exceed emission limits.

Is the P20BB code specific to certain engine types?

While not exclusive to them, this code is primarily associated with diesel engines equipped with SCR systems.

Can extreme weather conditions trigger the P20BB code?

Yes, very cold temperatures can sometimes trigger this code if they affect the DEF system’s operation.

How often should the reductant heater be inspected or replaced?

There’s no set schedule, but it should be inspected during regular maintenance. Replacement is typically only necessary if a fault is detected.

Can using low-quality DEF contribute to the P20BB code?

While not a direct cause, low-quality DEF can lead to system issues that may indirectly contribute to this code.

Will a P20BB code affect my vehicle’s performance?

Yes, it can lead to reduced engine performance and fuel efficiency, and in severe cases, may cause the vehicle to enter a “limp mode.”

Is there a temporary fix for the P20BB code?

There’s no reliable temporary fix. The underlying issue needs to be properly diagnosed and repaired to resolve the code permanently.