Wideband oxygen sensor upgrade

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Ignitron ECU needs a wideband oxygen sensor for the lambda regulation and adaptation to work. Without lambda regulation it is practically impossible to dial in fueling which can lead to engine failure (due to mixture being too lean or too rich). If your car (pre 2001 model year) is equipped with a narrowband oxygen sensor, it has to be upgraded to use a BOSCH LSU 4.2 wideband sensor! This involves replacing the sensor itself, replacing the mating female connector (from 4 pins to 6 pins) and adding and wiring two additional wires into the ECU.

You can buy the female connector from various webshops selling automotive connectors, the OEM VW part number is: 1J0-973-733 for the connector and 000-979-133E for the wire with a pin on it. As for the sensor, we recommend genuine BOSCH LSU 4.2 units only (avoid cheap counterfeits!), part number for reference is: 021-906-262-B (BOSCH part#: 0258007057), but this sensor is available under other part numbers, too (with different wire lengths).


Connectors for the narrowband sensor (facing front)
Sensor side (male) and chassis/car side (female)
Pinout and destination ECU pins for the narrowband sensor:
1: +12V Probe heater +
2: ECU 5 Probe heater -
3: ECU 51 Nernst cell ground
4: ECU 70 Nernst cell voltage output



Connectors for the LSU 4.2 wideband oxygen sensor (facing front)
Sensor side (male) and chassis/car side (female)
Pinout and destination ECU pins for LSU 4.2 wideband oxygen sensor:
1: ECU 70 Nernst cell voltage output
2: ECU 71 Calibration resistor
3: +12V Probe heater +
4: ECU 5 Probe heater -
5: ECU 51 Nernst cell and oxygen pump common ground
6: ECU 52 Oxygen pump drive



Pull purple lock out of the connector on the loom to access wiring assembly.


Pull the complete wiring assembly out!
Do not worry, individual wires cannot come out, they are locked by a tiny tab.


Connector of Ignitron ECU (facing front)
The wires from the LSU 4.2 wideband oxygen sensor need to be connected to the following ECU pins:
Sensor 1 -> ECU 70
Sensor 2 -> ECU 71
Sensor 3 -> Switched +12V (supplied by the fuel pump relay)
Sensor 4 -> ECU 5
Sensor 5 -> ECU 51
Sensor 6 -> ECU 52

There are only 2 additional wires (compared to the narrowband setup), ECU pin 52 (oxygen pump drive) and ECU pin 71 (calibration resistor), the other 4 wires of the narrowband sensor are connected to the appropriate pins at the ECU side. Either you add these two wires only, or replace all. Switched +12V for the probe heater is supplied by the fuel pump relay (and not by the engine ECU)! There should be a lot of unused ECU pins available in the connector assembly to use for extra wiring, however these need to be soldered - cannot be crimped, crimpable alternatives are TE Connectivity 166500-2, 909-7252 for example. Pins can be pulled out after folding the locking tab using a tiny screwdriver.

LSU 4.2 or 4.9?

Ignitron ECU (above hardware version 1.94) is compatible with both LSU 4.2 and LSU 4.9 wideband oxygen sensors, however, if you need to do an upgrade, we suggest you to go for the LSU 4.2 (OEM sensor for 1.8T is LSU 4.2). This article covers instructions on doing the upgrade to LSU 4.2! Please note, that the pinout and the connector for the LSU 4.9 sensors are different! Software settings are also completely different for the LSU 4.2 and LSU 4.9, the LSU 4.9 can get damaged if used with the settings of the LSU 4.2! If your car/wiring is equipped or prepared to use the LSU 4.9 probe (f.eg 2005+ R32), you do not need to modify it, just make sure you use the settings for the LSU 4.9!