Bosch LSU4.2 WBO2 Sensor
Holley replacement WBO2 sensor. #554-101
The actual wire (cable) length is 25", not including connector or sensor body. (Bosch LSU4.2 WBO2 Sensor Specifications)

NTK L2H2 WBO2 Sensor
Holley replacement WBO2 sensor. #554-100
The NTK WBO2 sensor is slightly more accurate, withstands higher
exhaust heat (forced induction) and is compatible with methanol/race fuels.

The actual wire (cable) length is 25", not including connector or sensor body.
FYI: The NTK WBO2 sensor is now the same length as the Bosch WBO2 sensor.

Holley WBO2 sensor 4' long extension harness
For Holley's Bosch LSU4.2 and NTK L2H2 wideband sensors. #534-199

• If a miswired wideband O2 sensor harness connector is suspected, verify it with the PIN-OUT below.
Seven wire Bosch WBO2 sensor connector:
C...brown - Calibration resistor in a shell, 2" down from connector. (Early Bosch sensors didn't have these two brown wires.)
D...brown - Calibration resistor in a shell, 2" down from connector. (Early Bosch sensors didn't have these two brown wires.)
H...(not used)

Seven wire NTK WBO2 sensor connector:
C...brown - Calibration resistor in a shell, 2" down. (Early NTK sensors had a shorter harness without these two brown wires.)
D...brown - Calibration resistor in a shell, 2" down. (Early NTK sensors had a shorter harness without these two brown wires.)
H...(not used)

Eight WBO2 sensor wires from ECU, at sensor connector (Bosch & NTK):

Eight WBO2 sensor wires at the ECU P1A connector
(Bosch & NTK):
WB1 HTR -......A9....yellow
WB1 COMPR1...A16...brown
WB1 COMPR2...A7....tan
WB1 VS-/
WB1 IP+.........A33...white
WB1 SHIELD....A8....shield
(Optional 2nd WBO2 sensor wires are pinned the same, at Dominator ECU P2A & at sensor connector.)

Abbreviation Definitions:
"HTR" ....= heater
"COMPR" = compensating resistance
"IP" .......= pumping current
"VS" ......= voltage source
"SHIELD" = drain wire

Abbreviated Voltage:
"HTR+ & -" ....= sensor's heater
"COMPR1 & 2" = calibration resistor
"VS-/IP-" ......= common ground
"IP+" ............= current source to sensor
"VS+" ...........= voltage input from sensor

Wideband O2 Sensor Notes:
• If configuring a new Global File or changing to a different wideband O2 sensor type (Bosch/NTK), be sure to leave the WBO2 sensor(s) disconnected, until you've programmed the correct "Wideband O2 Sensor Type" in the EFI software - Engine Parameters (in System Parameters). According to the warning label on new WBO2 sensors, if the ECU is powered on with the wrong WBO2 sensor selected, damage will occur. Aside from correct software programming, ensure there are no ignition misfires or exhaust leaks upstream of the WBO2 sensor(s).

• Large duration (race) camshafts will exhibit a fluctuating AFR/false lean condition at idle & low RPM, due to their significant amount of overlap. This also happens if there isn't a sufficient length of exhaust piping beyond the WBO2 sensor(s), due to the WBO2 sensor being near an open exhaust pipe (ambient air contamination). To rectify this, enter the Closed Loop Parameters (in System Parameters), and set the "Enable RPM to Enter Closed Loop" high enough to ignore this idle/low RPM condition. You'll then need to manually tune the idle area in Open Loop mode.

• The Advanced Control (1-5) sets how fast the Closed Loop control operates. 1 is the slowest and 5 is the fastest. (The Avenger & Terminator hand-held controller calls this the "Closed Loop Speed".) This also depends on where the WBO2 sensor is located in the exhaust system. The further away the WBO2 sensor is (away from the engine), the lower the number should be. If Advanced Control 4 or 5 is selected, one must ensure the ECU isn't oscillating the Closed Loop operation. Viewing a datalog is helpful. I experienced a condition where the actual AFR often "lagged" momentarily, behind the Target AFR. I fixed it by changing the Closed Loop Advanced Control to 4. My WBO2 sensors are located in full-length header collectors.

• If you suspect a failed WBO2 sensor, and your Fuel Table is well tuned, you can disable Closed Loop (in System Parameters), and the engine should run fine until a replacement WBO2 sensor arrives. You can do this to determine if the WBO2 sensor is at fault (at least at idle), because in Open Loop mode, the ECU ignores the WBO2 sensor. So if the engine starts running good in Open Loop mode, you've found the problem. Just ensure that you don't disable Closed Loop mode while the Learn Table is corrupted from a failed WBO2 sensor. Clear the Learn Table (if the percentages are erroneous from their nominal values), or upload the last "known to be good" Global File. You can't just replace the WBO2 sensor, and restart the engine. You must upload the last "known to be good" Global File, upload the base calibration, or at the very least, clear the Learn Table of the corrupted values from the defective WBO2 sensor. Also, if the ECU detects a WBO2 failure, it will go into Open Loop mode (no Closed Loop or Learning).
Read 6th paragraph: (Holley EFI Tuning Tips & Information)

• If you experience a failed WBO2 sensor on a fairly new EFI installation (low miles or repeated WBO2 sensor failures), ensure the current WBO2 sensor location (not angular position) isn't causing damage by exhaust condensation thermally shocking the sensor at startup and/or during the warmup period. If you suspect it is, install a sensor bung at a better location, use a taller O2 sensor bung or use an Innovate Motorsports HBX-1 to move the sensor probe out of the direct exhaust stream. I've been successfully using the Innovate Motorsports HBX-1 Heat-Sink Bung Extenders for many years (LINK), and I love these things. I won't use a WBO2 sensor without one. FYI: I didn't add indexing washers to the HBX-1. I just shaved down the one thick copper washer (included), until it turned enough for the machined dot (on hexagon) to face forward. (Additional WBO2 Bung Information)

This is referring to the "wet" gases flowing through the exhaust system while the engine is cold. On most vehicles, you can literally see water spitting out of the tailpipe(s). It's imperative to prevent this water from contacting the WBO2 sensor, because it will thermally shock the heated sensor. OEM engineers go to great lengths to locate the WBO2 at its optimum location. Anyway, a poor sensor location can actually blow water directly at the sensor probe. Look at the routing direction (angle) of the exhaust pipe just ahead of the sensor. Does it "direct" the water right at the sensor or away from it?

Diagnose The Following:
All sensor values correct on Data Monitor?
Failed WBO2 sensor corrupted Learn Table (unusual %)?
Exhaust leaks upstream of the WBO2 sensor?
Sufficient length of exhaust piping beyond WBO2 sensor?
Ignition misfire? (WBO2 sensor will read lean.)
Battery/charging system functioning properly?
Consistent fuel pressure? (Disconnect vacuum hose to measure static psi.)
Inspect wire harness/connectors for damage and ensure it's not near any high voltage components.

At key-on (initializing) and heating, the WBO2 sensor "LED" status indicator is yellow.
Then there shouldn't be any "LED" status indicator at all (especially when engine is running).
The WBO2 sensor heating cycle will time-out (key-on/engine-off) if the engine isn't started.
When the WBO2 sensor heating cycle times-out (key-on/engine-off), it will display "init". (Sensor Diagnostics & Statuses) (Ensure battery is fully charged!)
Key-on/engine-off & cold, the NTK WBO2 sensor displays about 29:1 AFR. The Bosch WBO2 sensor displays about 35:1 AFR.
After turning the engine off, exhaust gases need to dissipate before seeing these full lean AFRs (key-on/engine-off & cold).

Troubleshooting & Testing: (Sensor Diagnostics & Statuses) (Holley EFI Wiring Manual & Diagrams) (Troubleshooting Checklist - Holley EFI) ("Test Relay" for troubleshooting/diagnosis.) (Wideband O2 Sensor Test/Diagnosis - it works!)
If testing the WBO2 sensor key-on/engine-off, the sensor heater will time out, so you'll need to work fast.
If you need more time, the WBO2 sensor test can be performed with the engine running in Open Loop mode.

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Quote Originally Posted by Klaus Allmendinger, VP of Engineering, Innovate Motorsports
Differences between Bosch LSU4/4.2 and NTK UEGO
1) Response speed:
Measured by the sensors own response delay between pump cell and sense cell-
Bosch ~5 msec
NTK ~50 msec
I'm referring to the internal delay of the sensor between a change of pump current to change of measurement cell output for a constant AFR gas, not the delay between gas change and measurement cell output. The delay I stated is the impulse response of the control input (pump current) to measurement output.
2) Back Pressure sensitivity:
Bosch sensor has about 1/3 the NTK's pressure sensitivity.
Pressure sensitivity means that the sensor reads richer than reality in a rich mixture, leaner in lean mixture.
3) Temperature sensitivity:
NTK sensor is fairly insensitive to temperature either at bung or EGT, can run with constant heater voltage.
Bosch sensors are very sensitive and needs to have precisely controlled cell temperatures. Bosch sensors are sensitive to housing temperature.
4) Heating time:
NTK ~60 seconds
Bosch ~20 seconds
Warmup times are greatly influenced by additional heating by exhaust gas and can be shorter than what I stated. The numbers I posted are warmup times for the sensor in 20°C (68°F) still gas, sensor at 20°C (68°F), heating to full operating temp (useful measurements). Warmup cycle controlled to max warmup ramp as per respective manufacturer specs. In an actual engine situation (additional heating by exhaust gas) the Bosch can warm up in as low as 10 sec while still staying within the warmup ramp specs. The NTK can warmup in 33 secs or less. But these numbers are very much dependent on the engine situation (RPM, EGT) and therefore hard to compare and control.
5) Thermal shock:
There's no difference. The Bosch sensor is actually shrouded heavier than the NTK, which protects it a little better. The only difference I have seen is that the NTK often does not fail as dramatically and obviously as the Bosch, but can give you readings that are 1-3 AFR off.
This generally true from my experience with the NTK. It fails just as often and for the same reasons as the Bosch unit, but the failures are less noticeable. But it IS a lot slower due to its construction and can handle more mechanical abuse (banging it around).

Differences between Bosch LSU4 (066) and LSU4.2 (057/058)
1) Heater response time:
066 sensor has higher thermal mass and responds slower to heat input. This makes the 057/058 sensor a little bit more challenging to control, heater PID must react faster.
No problem in the LM-1, because it's already designed for the faster response of the 057.
2) Sensor tolerances:
066 sensors have tighter tolerances between sensors. This is not an issue with the LM-1 because it is calibrates to the individual sensor when doing a free air calibration.
3) 066 sensor is slightly more tolerant to overheating of the sensor housing at the bung. It takes longer to give completely erroneous values, but has the same specs.
4) 066 sensor is more expensive.
5) Connector is different.

Heat & Back Pressure Aspects:
It's all really simple. A narrowband sensor does not care about heat or back-pressure very much. It just needs to be at it's minimum temp (~300°C/572°F) to operate. It switches at 14.7 AFR between a low voltage (lean) and high voltage (rich). That's all it does. If people post that they have different readings on an NB sensor before and after turbo, it's because they use the NB sensor for what it can't do, namely measure AFR outside it's 14.7 +- ~0.3 AFR range. It's output voltage on the rich side just varies mainly with EGT (and just a little with AFR), that's all.
A wideband sensor IS sensitive to back pressure. Some more, some less. With back pressure a WB reads richer than reality on the rich side of stoichiometric, leaner than reality on the lean side. The NTK sensor is actually much more sensitive in that respect than the Bosch. The NTK sensor on the other hand is less sensitive to heat, and could theoretically take the pre-turbo heat. But the ECU needs to compensate for the wrong reading due to back pressure. OEMs do that by finding the appropriate compensation factors based on engine state.
The gist of it is that you can mount a narrowband sensor before the turbo, because it can take the heat and is ignored at WOT anyway. But even a heated NBO2 does not have a heater strong enough without help from EGTs to keep at it's operating temp in all conditions.
Mount a WB sensor downstream, for accurate measurement and sensor life. In the location designed for a NBO2 you will typically be asking for trouble.

Regarding Bosch LSU4.2 Location:
The Bosch LSU4.2 sensor has a specified housing temperature (at the bung) of max 560°C (1040°F). Exceeding this can cause problems because the heater in the sensor can no longer be precisely controlled. It does not destroy the sensor (typically), but AFR readings will be inaccurate because of uncontrolled sensor temperatures.
On many turbo cars the bung temperatures are higher than that. Same can happen with superchargers, wrapped/coated headers and pipes.
Narrowband O2 sensors are not very sensitive to heat, because they only need to work as a switch, not as a measurement device.
In many cases the bung temperatures of a NBO2 sensor location are much higher than the Bosch sensor can tolerate.
We (Innovate) found that although the sensor head can handle up to 1560°F EGT, bung temperatures are typically the bigger problem. That's why we recommend a heat sink for high bung temp applications.
The sensor head is temperature controlled. If heated to or above its operating temperature it can no longer be controlled (the sensor heater cannot cool). In that case in an OEM application for the sensor (closed loop WB control) the ECU goes open loop. A WB meter cannot go open loop (unfortunately) and either becomes inaccurate or shows an error (the LM-1 shows an error).
• As for warmup of the sensor:
This is key to the lifespan of the sensor. The LM-1 uses a controlled heat-up profile at the max. allowable heat-up rate that Bosch specifies for the sensor. Heat-up time in room temperature air is about 20 sec.

Sensors get destroyed for four reasons:
1) Carbon fouling
Happens when the sensor is left unpowered during engine warmup or running continuously at excessively rich mixtures (<10 AFR).
2) Lead fouling
Lead will at any temperature over time coat the pump cell ceramics and prevent it from working.
3) Penetrants
Things like WD-40, even traces of it, will destroy the sensor instantly because of a chemical reaction between the penetrant and the sensor ceramics.
The sensors get their reference air through the cable sheath. Penetrants can work their way through the cable into the sensor. After all, that's what penetrants are for.
4) Running the sensor outside specified temperatures.
This does not destroy the sensor instantly, but reduces its lifespan significantly.
Regards, Klaus