The P20D4: Exhaust Aftertreatment Fuel Injector ‘B’ Control Circuit High refers to a condition where the voltage in the control circuit for fuel injector ‘B’ is higher than expected. This may cause the fuel injector to malfunction, leading to improper fuel injection and potential emissions problems. The issue could stem from faulty wiring, a defective injector, or a malfunctioning control module.
P20D4 – Quick Overview
Code | Information |
---|---|
Meaning | P20D4: Exhaust Aftertreatment Fuel Injector ‘B’ Control Circuit High |
Is it serious? | Yes, this can cause improper fuel injection, affecting emissions control and vehicle performance. |
Possible causes | – High voltage in the fuel injector ‘B’ control circuit – Faulty fuel injector ‘B’ – Faulty control module |
How to diagnose? | – Measure voltage in the injector control circuit – Test the fuel injector ‘B’ – Check the control module functionality |
P20D4 Meaning
The P20D4 fault code indicates that the voltage in the control circuit for fuel injector ‘B’ is higher than it should be. This excessive voltage can cause the injector to malfunction, leading to overfueling or improper injection, which can affect the vehicle’s exhaust aftertreatment system and emissions. The issue may be due to electrical faults, a failing injector, or a malfunction in the control module.
Step-by-step diagnostic guide
Action | Description | Tools Needed |
---|---|---|
Check for Other Codes | Use an OBD-II scanner to check for additional related codes that might give further insight into the high voltage issue. | OBD-II Scanner |
Measure Voltage in the Injector Control Circuit | Use a multimeter to measure the voltage in the control circuit for fuel injector ‘B’ and confirm it is within the manufacturer’s specified range. | Multimeter |
Test Fuel Injector ‘B’ | Test fuel injector ‘B’ using a diagnostic tool to ensure that it is not malfunctioning due to the excessive voltage. | Multimeter, Diagnostic Tool |
Check the Control Module | Verify that the control module is functioning correctly and is not causing the high voltage in the control circuit. | Diagnostic Tool |
Repair or Replace Wiring/Injector | If high voltage is detected, inspect the wiring for shorts or other electrical faults, and repair or replace the injector as needed. | Wiring Kit, Replacement Injector |
Clear the Code and Test Drive | After repairs, clear the code using an OBD-II scanner and take the vehicle for a test drive to confirm that the issue is resolved. | OBD-II Scanner, Vehicle Manual |
Recheck for Codes | After the test drive, rescan the vehicle to ensure the P20D4 code does not return. | OBD-II Scanner |

OBD-II scanner Buyer’s Guide
- Scanner features explained
- Different types of scanners
- Scanners for coding/odometer/ECU/checks
- Best picks + discount codes

Hi, I am Juraj “Yuri” Lukacko. I got frustrated by unhelpful and scammy mechanics, so I decided to learn everything about car diagnostics myself. I test dozens of new car diagnostic tools every month along with learning new strategies to fix and customize cars. About Juraj Lukacko (Yuri)