If the NOXEM probe is damaged, it is possible to replace it by yourself.

Note: At first, eliminate all causes for the probe getting damaged! Typically – leaking injectors. Less often – increased oil consumption of the engine; mechanical damage of the probe; water in the exhaust system or HPFP/LPFP problems; other Lambda probes, etc. If the causes are not eliminated, the new probe will be damaged soon! 

NOXEM uses the following components:

1. Lambda probe: Bosch LSU 4.9 wideband 5 wire probe. Bosch Code: LS 0 258 017 025 (and 1:1 analog LS 0 258 017 099, developed for BMW); depending on availability in manufacturer stocks.

2. Thread insert VS5281R (M18 to M20 X 1.5mm)

Choice of the Lambda probe

The probe mentioned in P.1 is the most robust and most expensive solution. As a budget solution, Bosch LSU 4.9 probes (intended for Mazda, Opel, VW, etc., repairs) will do.

Note: data reported by the NOXEM should be accurate, so China-made “alternative” probes can not be used! Watch out for fakes! Keep in mind that the original probe’s recommended shelf price (Motorsport edition) goes over EUR 200!

Thread insert

OEM NOx sensor thread size is M20 X 1.5mm. Bosch LSU 4.9 thread size is M18 X 1.5mm. To adjust the boring hole size with the NOXEM, thread insert M18 to M20 is used. This threat insert was placed on the NOXEM probe when you purchased it. It is possible that you did not even notice it. 

If, after removing the damaged Lambda probe, the thread insert is left in the exhaust, you can screw a new Lambda probe in place of the old one. In this case, you don’t have to worry about mechanical compatibility.  

If the thread insert has stayed on the probe after removing the old probe, you will have to purchase and attach a new insert. Such thread inserts are intended to repair the boring holes of the Lambda probes, and they can be purchased in any larger shop of car parts. The only thing you have to know: M18 to M20 (threat step: 1.5mm).

Replacing the NOXEM probe

1. demount the NOXEM, 30 .. 50cm from the probe, cut the wire to the NOXEM unit.

Note: the NOXEM is sealed, so the replacement of the wire inside it is not possible. 

2. cut the connector of the new Lambda probe

Note: for all Bosch LSU 4.9 probes, the identical color of the wire is used. Wires are white, grey, black, yellow, and red.

3. solder the wires

Note: for the soldering of wires, it is recommended to use a soldering acid/paste, for example, Weller lotfett soldering grease.

To insulate the wires, use thermal insulation tubes.

4. put on the thermal insulation tube on each of the wires. Put on the larger/common thermal tube on the whole cable. Solder the wires. White with white, black with black, etc. Seal each wire, heating up the thermal tube. Seal the complete cable, heating up the large thermal tube. 

5. screw in the new Lambda probe in the exhaust system.

With this, the repair of the NOXEM is completed.

If you wish, you can modify the repair. This option will make the repeated replacement of the probe easier (if it will be necessary):

1. cut off the old Lambda probe;

2. purchase the LSU 4.9 connector kit and solder it to the NOXEM wire

Here, how such an upgrade looks like:

After such a repair, the replacement of the probe will take only 20 .. 30 minutes!