From Aug 2014

Issues with lambda getting "stuck" at 0.83

Issue with lambda getting stuck when doing a power pull, issue started out of no where and consistently getting worse so the point that I can no longer read lambda under large loads.

Wiring has been checked, and re-checked... Sensor is new.

Sensor had a hard time to calibrate at the beginning (seemed like heater wasn't activating correctly all the time under calibration) I had to start/stop the calibration process a few times in order to get the O2 heater activated for free air cal. Seemed to read fine otherwise and is accurate under light loads @ idle.

Screen shot of log:


Lambda sensor eventually recovers in approx 2-3 seconds of overrun:


Update - Aug 2016

Late last year the owner replaced the WBO2 w/ a new sensor and let me know that it calibrated ok. I wrote the lambda issue off to the sensor after all.

2 Days ago, pre-test race w/ swapped to E98 (from E85) and I noticed the WBO2 was not working at all again. After numerous attempts of free air calibration with the new sensor, the original sensor and one brand new never used O2 sensor. All 3 sensors had the same issue. During calibration the heater would never start heating.

Checked wiring again, everything checks out, 12V source is good. I did not have my resistors with me to check the WB output from the ECU so I swapped to a known good ECU and the issue was solved.

It's clear the customers ECU has a defect from HU. Unfortunately it is outside of the warranty period now, but I will be bench testing the ECU and hopefully can be guided to do the repair on the ECU. I'm hoping it is maybe just a bad solder point or driver/IGBT for the WB heater.


I have bench tested the ECU with the following results:

Following test steps listed here:

Voltage test / ECU ON / WBO2 ON (Heater):

Pin 5 (pump -) + GND = 3.98V (no change to this when adjusting pw_zero up or down - w/ burn + restart of ECU)

Pin 1 (nernst) + GND = 4.41-42V

Pin 1 + Pin 5 = 0.445V

GenBoard/Manual/WBSensorControllerTesting steps:

Voltage Test / ECU ON / WBO2 OFF (Heater):

pump- = 0.0V

GND = -3.97V (again no change when adj. pw_zero)

Voltage Test / ECU ON / WBO2 ON (Heater):

pump- = 0.0V

nernst+ = 0.445V

pump+ = 0.910V

All tests done with correct 100 ohm resistors as stated in the links.

ECU SN: 8501

sometimes it happens that exhaust is blocked and then lambda fails

Dave reviewed config, all defaults applied no config issues found

Please let me know the next step.. this box is still not working, where the other VEMS box works perfectly fine without issue with the same CFG and any FW.

Review of v3.3_u008501-2017.06.15-22.25.52.vemslog:

If you provide measurements to each of the measurements Q's above we should be able to locate the cause of the issue. Thanks!

Best regards, Dave

Test results

Checked all wiring again, 12V is good, continuity is perfect 0.1 ohm between EC plug and WB plug.

Test results from pin 4 as requested are shown the picture with the WBO2 off, it shows stable battery voltage.

With the Auto calibration on during initial heating phase, voltage slowly drops from batt V. to about 7V, then when I suppose it is trying ti maintain the heater you see oscillation.

You can see in this video (missing the V drop from the heating stage):

That said, I really don't have anymore time for these tests.

This ECU is bad and needs to be repaired, and this issue has been present from the beginning since it was sent to me. There are races to be raced this year and I need a fully functioning ECU please.

If another ECU works perfectly fine is the harness and many O2 sensors, then regardless what is found or not found, it must be the ECU's fault.

Hello Sascha

Sorry for my delayed feedback on your measurements and findings (i was on holiday), my conclusion matches yours some problem with heater control inside the ecu is likely.

Please fire a Ecu Repair/Upgrade order in WebShop using this page:, linking to this wiki page for reference of your case and tests.

Best regards, Dave

Hi Dave,

thanks for the reply, we all need some time off :)

I process this asap on the webstore with a link to this page.

For notes regarding the ECU to be fixed, I would like to request the following updates to the ECU: