For Volkswagen TDI owners with the ALH engine, disabling the Exhaust Gas Recirculation (EGR) system is a common modification. This guide outlines a cost-effective method to perform an EGR delete using a relay and resistor, costing around $10 and requiring basic automotive DIY skills. This method effectively tricks the engine control module (ECM) into thinking the EGR system is functioning correctly, preventing check engine lights (CEL) and maintaining optimal engine performance after physical EGR valve removal or blockage.
To begin, disconnect the EGR valve solenoid connector. This circuit will be repurposed to control a Single Pole Double Throw (SPDT) relay (terminals 85 and 86). For a clean installation, consider sourcing a compatible connector from a salvage yard. You can then solder wires from the relay to this connector, creating a plug-and-play solution that avoids splicing into the original vehicle wiring harness.
Next, locate wire number 4 on the Mass Air Flow (MAF) sensor plug – this is the wire closest to the engine on an ALH TDI. This wire is typically twisted with wire number 3. Cut wire number 4 and connect the MAF sensor side of the wire to terminal 30 on the relay. The remaining wire, leading to the ECU, needs a “Y” connection. Connect one branch of this “Y” to relay terminal 87a. For the other branch, incorporate a resistor (a 1/2w 5.6K ohm resistor is suitable) and connect it to relay terminal 87.
This wiring configuration ensures that when the EGR solenoid circuit is inactive (de-energized), the MAF sensor readings are normal. However, when the EGR solenoid circuit becomes active (energized), the relay also energizes. This introduces the 5.6K ohm resistance into the MAF sensor circuit, causing the ECM to perceive a reduced airflow – mimicking the effect of an open EGR valve.
While an adjustable potentiometer could be used to fine-tune the resistance for a precise match between actual and requested airflow, a fixed 5.6K ohm resistor often proves sufficient to eliminate CELs and achieve the desired EGR delete effect, as tested using VCDS (VAG-COM Diagnostic System). VCDS readings should reflect normal EGR operation in graphs, with airflow readings decreasing when the relay is energized and returning to normal when de-energized, confirming the successful EGR delete modification.
