Lambda probes. Introduction

What is Lambda?

Lambda (AFR) is characterizing relationship of air/fuel ratio. For example, Lambda 1.00 is Stoihiometric mixture (14.7/1); Lambda 2.00: 29.4/1 (lean), Lambda 0.90: 13.2/1 (rich), etc.


How does Lambda affect the performance of the engine?

a) Lambda 1.00: a compromise between performance and exhaust emissions (CO/CH);

b) Lambda 0.90: max power, increased CO/CH;

c) Lambda over 1.40: for the regular engine – misfires (mixture don’t ignite);

d) Lambda 1.4 .. 3.0: is used only for direct injection engines, which are performing in Stratified charge;

e) Lambda >10: overrun mode (only air in the exhaust).


What Lambda is maintained by BMW petrol engines (in work temperature)?

a) Lambda 1.00: driving evenly (except N43/N53);

b) Lambda 0.80 .. 1.00 kick-down mode.


N43/N53 series engines, driving evenly:

a) Lambda 1.00: (Homogeneous mode);

b) Lambda 1.40 .. 3.00: (Homogeneous lean/Stratified charge injection).


What are basic types of Lambda probes used in cars?

a) narrow-band probes (are able to measure Lambda 0.99 .. 1.01);

b) wide-band (are able to measure Lambda at least 0.80 .. 16.00).


What probes are used by BMW?

After catalytic converters, always narrow-band Lambda probes are used.

Before catalytic converters:

a) narrow-band probes for M series petrol engines;

b) wide-band probes for N series petrol engines.


What voltage range is correct for each type of probes?

a) narrow-band probes are producing a voltage of 0.00 .. 0.90V;

b) to manage wide-band probes, special electronic solutions are used, the voltage of the output of these units changes 0.0 .. >4.1V.


How to interpret voltage, which is displayed by Lambda probes?

Narrow-band probes:

a) voltage <0.10V: fuel mixture is lean (Lambda >1.00);

b) voltage >0.70V: fuel mixture ir rich (Lambda <1.00).


Wide-band probes.

Bosch management units:

a) 1.50V: Lambda is 1.00;

b) <1.50V: Lambda <1.00 (mixture is rich);

c) >1.50V: Lambda >1.00 (mixture is lean);

d) >4.00V: Lambda >16.0, overrun mode (exhaust gas – air).


Siemens management units:

a) 2.00V: Lambda is 1.00;

b) <2.00V: Lambda <1.00 (mixture is rich);

c) >2.00V: Lambda >1.00 (around 2.50V, if Lambda 2.00; around 3.00V, if Lambda 3.00; mixture is lean);

d) >4.00V: Lambda >16; overrun mode (exhaust gas – air).


Correct indications of narrow-band probes for the heated-up engine in idle and driving evenly:

a) before catalytic converters (M series engines): periodically (once in a second/in two seconds) changes from <0.10V to >0.70V and back;

b) after catalytic converters (except N43/N53 engines): 0.70 .. 0.80V continuously (if CO catalytic converters are in work order).


N43/N53 series engines:

a) 0.70 .. 0.80V continuously (if CO catalytic converters are in work order), if wide-band probes show Lambda around 1.00 (the engine works in Homogeneous mode);

b) <0.10V, if wideband-probes show Lambda 1.4 .. 3.0 (the engine works in Homogeneous lean or Stratified charge modes).


Related entries:

Lambda probes. Wideband

Management of Lambda probes

MSV70/80; MSD80 and Lambda probes. Hidden defects

Wide-band probes. Hidden defects. Part 2