The Exhaust Gas Recirculation (EGR) system in your ALH TDI engine is designed to reduce NOx emissions by recirculating exhaust gases back into the intake manifold. However, over time, the EGR system can become problematic, leading to carbon buildup, reduced engine performance, and potential component failures. For off-road or track use where emissions regulations are less stringent, many ALH TDI owners consider an EGR delete. This guide provides a cost-effective and straightforward DIY method to perform an EGR delete on your ALH TDI using a relay and resistor, preventing check engine lights (CEL) and maintaining optimal engine operation.
Understanding the ALH TDI EGR Delete with Relay and Resistor
This method leverages a simple electrical circuit modification to trick the engine control unit (ECU) into thinking the EGR system is functioning normally, even after physical removal or disabling. By using a relay and resistor, we can simulate the electrical signals associated with EGR operation, thus avoiding error codes and CEL illumination. This approach is a budget-friendly alternative to ECU tuning or more complex EGR delete kits.
Parts You’ll Need for the ALH TDI EGR Delete
Before starting, gather the necessary components:
- SPDT Relay: A Single Pole Double Throw relay will be used to switch the MAF sensor signal.
- Resistor: A 5.6K ohm, 1/2 watt resistor is recommended to simulate the EGR flow reduction.
- Wire: Sufficient length of automotive-grade wire for making connections.
- Connectors or Splices: Choose your preferred method for making electrical connections (solder, crimp connectors, or a salvaged connector as described in the original article).
- Basic Tools: Wire stripper, crimping tool (if using crimp connectors), soldering iron (if soldering), multimeter (optional but helpful for testing).
Step-by-Step Guide to Performing the ALH TDI EGR Delete
Caution: This modification is intended for off-road or track use only and may not be legal in your region. Proceed with caution and at your own risk. Disconnect the negative battery terminal before starting any electrical work.
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Locate the EGR Solenoid Connector: Identify and unplug the electrical connector going to the EGR valve solenoid. This connector will be used to trigger the relay.
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Wire the Relay (Terminals 85 & 86): Connect relay terminals 85 and 86 to the EGR solenoid connector wires. Regardless of polarity for most relays, but you can check your relay’s datasheet. This circuit will energize the relay when the ECU commands the EGR to open. You can splice into the wires or use a salvaged connector as mentioned in the original article for a cleaner install.
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Identify the MAF Sensor Wire #4: Locate the Mass Air Flow (MAF) sensor connector. On an ALH TDI, wire #4 (closest to the engine side) is the signal wire we need to modify. It’s often twisted with wire #3.
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Cut MAF Sensor Wire #4: Carefully cut wire #4 of the MAF sensor. This will interrupt the signal going to the ECU.
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Connect to Relay Terminal 30: Connect the MAF sensor side of the cut wire (the wire coming from the MAF sensor itself) to relay terminal 30.
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Create a “Y” Connection for the ECU Side of MAF Wire #4: The wire going towards the ECU (the other end of the cut MAF wire #4) needs to be connected to both relay terminal 87a and the resistor. Create a “Y” splice on this wire.
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Connect to Relay Terminal 87a: Connect one branch of the “Y” connection to relay terminal 87a.
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Connect Resistor to Relay Terminal 87: Connect the 5.6K ohm resistor to the other branch of the “Y” connection and then connect the other end of the resistor to relay terminal 87.
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Insulate and Secure Wiring: Ensure all connections are properly insulated with electrical tape or heat shrink tubing. Secure the relay and wiring neatly away from moving parts and heat sources.
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Reconnect Battery and Test: Reconnect the negative battery terminal. Start the engine and check for any CEL. Use a diagnostic tool like VCDS (VAG-COM Diagnostic System) to monitor MAF readings and EGR requested vs. actual values to verify the modification is working as intended.
How the Relay and Resistor Trick Works
When the ECU de-energizes the EGR solenoid (EGR “closed” state), the relay is also de-energized. In this state, the MAF sensor signal passes directly through terminal 30 and 87a of the relay to the ECU, providing a normal airflow reading.
When the ECU energizes the EGR solenoid (EGR “open” state), the relay is energized. This switches the MAF sensor signal from terminal 87a to terminal 87. Now, the MAF signal passes through the 5.6K ohm resistor before reaching the ECU. This added resistance lowers the voltage of the MAF signal, which the ECU interprets as a reduced airflow, simulating the effect of EGR valve opening and exhaust gas recirculation.
The 5.6K ohm resistor value is chosen to provide a signal change that is within the acceptable range for the ECU, preventing fault codes while effectively simulating EGR operation.
Conclusion
This DIY Alh Tdi Egr Delete method using a relay and resistor offers a simple and inexpensive way to disable the EGR system and avoid CEL issues. By understanding the wiring and the principle of signal manipulation, you can perform this modification effectively. Remember to always prioritize safety, double-check your wiring, and use appropriate tools for a successful and reliable EGR delete on your ALH TDI engine. Always consider the legal and environmental implications of EGR removal in your specific location.
