In this entry, I will summarize the damages of the wideband probes and will describe the identification of these defects, using diagnostics (live) data.
I will describe both regulating (pre-cat) and NOx sensor probes (in case of OEM and/or NOXEM). Menu references are of N43/N53 (E series) engines, but analogous are available for every petrol engine.
- Defect of the calibrating resistor (located in the plug). This defect is possible only for Bosch LSU 4.9 (4.2) probes. The fault is NOT possible for Bosch LSU ADV and for NOx sensors.
Cause of the defect
Lost contact with the calibration resistor in the probe plug.
Consequences of the defect
The sensitivity of the probe outside the Stoichiometric fuel mixture (with Lambda 1.00) is enormously increased. For example, instead of Lambda 1.10, the probe reports Lambda 1.30; instead of Lambda 0.95, the probe reports 0.82.
The probe erroneously corrects the fuel mixture, overcompensating of the fuel mixture correction; shivering, instability is possible. The error messages regarding fuel mixture (both lean and rich) are possible, the error messages regarding trim control of the probe, misfires. The switching of the DME to the open-loop mode also is possible.
Identification of the defect
Relatively simple for N53 (E series) engines, performing the test block of the probes. Difficult for other engines.
Actual menu
For N53 series engines: ../F9/F3. Correction Lambda of the pre-cat probes in the probe test block should be 0.90/1.10 (+/-0.02).
For all: ../F5/F6. Lambda indicates very high and swift discrepancies to the required. For example, in Homogeneous mode, Lambda swiftly changes above 1.00 +/-0.05.
Remarks
Nernst resistance (chemical efficiency of the probe): correct. - Damage of the active element of the probe (ceramic plate). Typically – microcracks, but also more severe defects are possible – even complete brake-up of the plate. The fault is possible for Bosch LSU 4.9 (4.2), LSU ADV, NOx sensor probes (both OEM and NOXEM).
Cause of the defect
Damage due to the thermal shock (water condensate in the exhaust) or consequences of the mechanical damage (mechanical hit to the exhaust or the explosion of unburned fuel).
Consequences of the defect
Permanent damage to the probe. The probe stops to work – it indicates Lambda 1.00 in all driving conditions. DME identifies inappropriate Nernst resistance, records the error message regarding the temperature (heating) of the probe, turns off its heating.
Identification of the defect
Simple for all engines. Probe indicates Lambda = 1.00 in all driving conditions (including Overrun), the status of the probe (ISTA D): Not ready. The status of the OEM NOx sensor: Not ready; the error messages regarding self-diagnostics. NOXEM reports Lambda binary 500 +/-10 mV, possible status (ISTA D): Not ready.
Actual menu
For pre-cat probes: ../F5/F6 Lambda is 1.00 all the time (including Overrun mode);
../F5/F2/F6 Nernst resistance corresponds the max value.
For OEM NOx sensors (Online mode): ../F5/Shift+F2/F1 Lambda binary constant (but different from 1200 mV); Lambda linear constant in all driving conditions (including Overrun).
NOXEM (Online mode): ../F5/Shift+F2/F1 Lambda binary 500 +/10mV; Lambda linear 1.00 in all dirving conditions (including Overrun). - Chemical poisoning of the probe. The defect is possible for Bosch 4.9 (4.2), LSU ADV, NOx sensor probes (both OEM and NOXEM).
Cause of the defect
The most common product of probe poisoning – unburned fuel. Less often – different chemical substances (fuel additives or sprays for exhaust cleaning, injected directly in the exhaust) or other sprays, which are used during to replacement of the probe of repair of the exhaust system (for example, WD40, etc.). The chemical poisoning creates the current leak in the Nernst cell of the probe, and it paralyzes the correct performance of the probe.
Consequences of the defect
The probe reference (by Lambda = 1.00) becomes inappropriate. Typically – the probe indicates increased Lambda (1.50 till clean air: 20 .. 30). The defect can be sporadic, it means – the probe sometimes “comes back to life,” but periodically, it gets “sick.”
Actual menu
For the pre-cat probes: ../F5/F6 Lambda value rapidly increases above the genuinely possible. It can reach a max value (16). If the warming up of the probe is turned off, the probe reports Lambda 1.00 in all modes (including Overrun).
For the NOx sensors (Online mode): ../F5/Shift+F2/F1 Lambda linear strongly increased, can reach max value (32).
Remarks
The chemical efficiency of the probe is correct. In case of small or average poisoning, “recovery” of the probe during a more extended period is possible (for the probe to “clean up” faster, it has to warm up till the working temperature). - Clogging of the probe. The defect is possible to Bosch LSU 4.9 (4.2), LSU ADV, NOx sensor probes (both OEM and NOXEM).
Cause of the defect
The “measuring” openings or the cells of the ceramic plate are mechanically clogged with burning products (typically – fuel contamination or oil), which have gotten in the exhaust. Accordingly – the air and/or fuel leftover don’t get (or gets only partially and only after a long time) in the probe. The probe gradually gets “slower” and “less sensitive.”
Consequences of the defect
The quality and precision of maintaining the fuel mixture get worse. The non-compliance of the reported Lambda = 1.00 to the true value is possible (both in the direction of rich or lean fuel mixture).
In case of a more obvious defect, DME records the error messages regarding trim problems of the probes; lowered Lambda in Overrun mode, slower response, plausibility.
Identification of the defect. The simplest is to test the ability of the probe to identify clean air in the overrun mode.
Actual menu
For the pre-cat probes: ../F5/F6; Lambda has to be 16 in the Overrun mode; reported Lambda – strongly decreased.
For the NOX sensors (Online mode): ../F5/Shift+F2/F1; Lambda linear has to be 15 .. 32 Overrun mode. Lowered Lambda till 8 .. 10 is allowed. Reported Lambda – significantly lower.
Remarks
The chemical efficiency of the probe is correct.
[1] defect of the calibrating resistor
[2] mechanical damage to the ceramic element
[3] poisoning of the probe
[4] clogging of the probe
[5] correct curve
