EfiO2Meter Wiring

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O2 Sensor and Accessories Wiring

The efiO2Meter is equipped with connectors to provide the electrical hook-up to the Bosch LSU 4.9 Wide Band O2 Sensor and various I/O connections. Please note : we also support the LSU 4.2 for legacy reasons, while the typical LSU 4.2 connector looks similar to the LSU 4.9 connector it is significantly bigger than the typical LSU 4.9 connector

we need to work on a whole bunch of pics and docs.. please be patience and give us some time.

We also supply any of the efiO2Meter specific wiring connectors and terminals, please visit us at ... not yet edited.

A little note : the O2 sensor connector is a bit tricky to assemble, and if anything goes wrong it becomes even way more complicated to disassemble and to correct the mistake ... believe us, we had to go through this by accidentally swapping wires and luckily catching the mistake before we would have hooked up the sensor and powered it on :)
Instructions on assembling and disassembling the connector are here ... placeholder, not yet buddy

The terminals are crimp type and would require either an appropriate crimp tool or needle-nose pliers to close the crimp portions and a solder iron to finally solder the wires for the pliers closed contacts to provide good electrical connectivity and mechanical strength.

While this page contains lots and lots of information, we have to start with something, so let's get going.

Below please find the schematics outlining the interface of the efiO2Meter to the outside world.
Any component values and gain and timing calculations might not be the final settings of the product since these are early documentation drawings and were cut out of the real schematics at earlier stages of the design process.

Vehicle Power Connection

The picture below is a sample of how to connect the efiO2Meter into a vehicle power wiring.

EfiO2Meter Vbatt Schema.png

  1. Connect Vbatt neg or a reliable vehicle frame or engine ground connection to the Relay Coil and to efiO2Meter connector J1.2 (Gnd).
  2. Connect Vbatt pos to the Relay Contact with an optional Fuse in the middle.
    Fuse rating should be 2 A to 2.5 A for an LSU 4.9 and 3 A to 4 A for an LSU 4.2 Sensor.
  3. Connect the other side of the Relay Contact to efiO2Meter connector J1.1 (12V)
  4. Connect the other side of the Relay Coil to either the ignition signal coming from the ignition switch, or to the 12 V supply rail for the fuel injectors.
  5. Connect a Diode (like a 1N400x or similar) in parallel to the Relay Coil to prevent Back-EMF spikes at Turn-Off on the 12 supply. Make sure the diode is switched against the 12 V flow, otherwise it would smoke the diode. The black, white, silver ... ring marking on a circular diode body indicates the Cathode, Bar on the diode symbol.

This now provides a direct 12 V switchable supply to the efiO2Meter.

Please use the external start switch in the Start-On position (switch Off to Gnd) since it is not advisable to have a non heated LSU 4.x sensor in the exhaust stream. Not connecting a start switch will also keep the efiO2Meter in start mode through an internal pull-up resistor.

efiO2Meter Main Connector, J1

This paragraph describes the functionality of the individual digital I/O circuits along with the 12 V DC power hookup.

EfiO2Meter IO 0 Schema.png

  1. Power and Ground Hookups :
    Connect pin J1.1 to a stable 12 V supply capable to deliver at minimum 3 A without any significant voltage drop (< 500 mV) or simply to the 12 V battery.
    Connect pin J1.2 to a solid ground also capable of carrying at minimum 3 A without any significant voltage drop (< 500 mV)
    Use pin J1.3 as additional ground also connected to the same source as pin J1.2. Use this pin also for the use with the signals on pins J1.4, J1.5 and / or J1.7, J1.8.
  2. RS232 Communication :
    The RS232 serial communications levels are provided by a MAX232 type IC chip and the operating parameters are as follows : 57600 Bd, 8 data-bits, No Parity, 1 Stop Bit, No Handshake.
    TxD pin J1.5, transmit needs to be connected to pin 2 receive on the standard DB9 serial interface connector.
    RxD pin J1.4, receive needs to be connected to pin 3 transmit on the standard DB9 serial interface connector.
    And ground pin J1.3 needs to be connected to pin 5 common ground on the standard DB9 serial interface connector.
  3. Measurement Start / Stop In :
    This digital input needs a switch closure against ground with switch open = measurement start (sensor heater on) and switch closed = measurement stop (sensor heater off).
    The other option is to supply an external voltage of > 4 V and < 16 V for measurement start, heater on or a voltage of < 2 V for measurement stop, heater off.
    Basically Measurement start (on) / stop (off) can also be seen as Sensor heater on / off.
    The same can be accomplished with the communications command zzz (specification needed) 1 for heater on and zzz 0 for heater off. This works only if the start / stop input is in the stop position.
  4. Error Out :
    Open MOSFET drain out with 100 ohm current limiting resistor (at 5 V max) and jumper selectable internal 2.2 k ohm pullup resistors for 5 V and 10 k ohm pullup resistor for 12 V.
    Error = 0 V, logic low ... can also be seen as System Ok on logic high.
    The error indicates an internal or sensor failure, which forces the heater off. after all failures have been cleared it will resume normal operation after a stop / start toggle.

A simple wiring example below shows the basics and signal name to pin # assignments for J1 and J2.

  • The Start / Stop Signal can also be an external DC voltage of 0 V (lo = start) to 5 V - 12 V (hi = stop)
  • In case of external powered Error circuit as shown, please remove Control Board Jumper J4.
  • For inductive loads (relay coils ... etc) please back-EMF protect the error out with a bypass diode.

EfiO2Meter IO 0 J1 J2.png

efiO2Meter Analog I/O Connector, J2

This paragraph describes the functionality of the individual analog I/O circuits along with the electrical interfaces.

EfiO2Meter IO 1 Schema.png

  1. TPS and Ext Analog Inputs :
    Both inputs have a voltage follower OP-Amp with an input impedance of 1 M ohm to ground and accept an input signal range of 0 V - 5 V.
  2. RPM Pulse Input :
    This input senses pulses within an amplitude range of 3 V - 24 V and a tRC of 0.07 ms transient filter time. This should allow a pulse-train coming from up to a max 64 pulses per 2 revolutions at 18000 RPM (0.10 ms / pulse).
    Config settings provide a pulse count per 2 revolutions setting.
    Qualifying RPM Sensors would be crankshaft sensor, camshaft sensor, primary ignition coil tap pulses if used with the ignition pulse attenuator dongle.
    we will support direct hookup of the rpm input to the primary winding of the ignition coil with an optional ignition pulse attenuator dongle (currently under development).
    also a high impedance pickup adaptor dongle for inductive crank shaft and cam-shaft sensors is planned.
  3. O2 Sensor Simulation Out :
    This circuit has an over-current protected rail to rail op-amp output (100 ohm) with differential inputs, where one of them is used as an external ground reference to base it's output signal on. The other input is for the "O2PWM" pwm signal coming from the CPU, being filtered by a Sallen Key arrangement. Not really necessary, but at the expense of a single cap and 1/2 of a resistor network ... why not. The stuffing (machine assembly) cost of a resistor is more than 5 times the price of a single resistor itself, which gives already a reason for the use of resistor networks.
    Back to the real world now. J2.7 carries the narrow band Simulated O2 Sensor output signal and J2.8 can be used as a virtual ground reference in case that the O2 sensor input of your ECU is not vehicle (engine) ground based. In other words it is a Ground Level Sense input. Normally tied to Ground at J2.6, or your ECU / engine ground. Do NOT leave it open floating ... it will NOT work this way. This reference ground needs to be connected and has about 400 k ohm input impedance. It is also sensitive to any static electricity spikes or transients, so please tie it to the appropriate ground connection and avoid any time to leave it floating.
    The O2 level or air / fuel ratio output trigger points as well as the output voltage levels for high and low are software programmable.
    This internal adjustment ranges are AFR 11.0 (0.75) to AFR 17.6 (1.20) and 0.0 V to 1.65 V
  4. O2 Level Analog Out :
    Identical to the O2 Sensor Simulation Out channel, except the internal adjustment ranges are AFR 9.55 (0.65) to AFR 441 (30.00) and 0.0 V to 5.0 V.
    And internal ground reference, use pin 4 as ground reference out.

efiO2Meter Sensor Connector, J3

The efiO2Meter controller board based sensor connector J3. contains the 6 signals to interface to the LSU 4.x sensor. It is basically a 6 pin shrouded 0.1" single row connector similar to J1. A 6 conductor cable will provide the connections from J3 to the LSU 4.x sensor.

  1. VM, Virtual Ground J3.1 :
    Sensor virtual ground connection, typically at 2.5 V
  2. UN, Volts at Nernst Cell signal J3.2 :
    Sensor Nernst Cell connection, typically at 2.5 V + 450 mV
  3. IA, Pump Cell Current Amplifier signal J3.3 :
    Sensor Ion Pump Cell Current input connection, 0.5 V to 2.5 V for Lambda < 1 and 2.5 V to 4.5 V for Lambda > 1.
  4. IP, Pump Cell Current Probe signal J3.4 :
    The controller board has a precision 61.9 Ohm series resistor connected at J3.3 to J3.4.
    The voltage drop across this current measurement resistors is measured and internally amplified by the CJ125 and provides the raw data for the Lambda calculations.
    It is therefore possible to measure the DC voltage between J3.3 and J3.4 with a mV-Meter and calculate the sensor pump current with the help of the conversion table contained in the LSU 4.x data sheets.
    Note : we do not recommend you to literally do this measurement, since the CJ125 does it for you and our firmware provides the calculations for you as well :)
  5. H-, Sensor Heater neg. signal J3.5 :
    This signal switches the sensor heater on a PWM basis to ground.
  6. H+, Sensor Heater pos. signal J3.6 :
    This signal provides the 12 V sensor heater voltage. It is fused with a 4 A soldered through-hole fuse (F51) ... so don't blow it unless you want to un-solder the blown one and re-solder a new one :)

A colorful sample wiring diagram shows the J3 to sensor signal name and pin assignments.

EfiO2Meter IO 0 J3.png

LSU 4.9, LSU 4.2 Sensor Connector pin-out

The following table shows that there are differences in the two LSU 4.x variants in the connector pin-outs for the same signals. Also be aware that the connectors differ in sizes largely, even on a picture they look exactly the same. It was a surprise for us as well when we got our 1st LSU 4.9 sensor after being used to the LSU 4.2.

LSU4.9 Connector :

Bosch 1 928 404 669

FEP 42121700

1J0 973 713 – 6 Way Sealed Female Connector 1.5 mm, 2-row, Coding I

others : 1813139-1 Mates with : 42064700

LSU4.2 Connector :

VW # 1J0-973-733

FEP 42122200

1J0 973 733 – 6 Way Sealed Female Connector 2.8 mm, 2-row, Coding I

others : 1J0 873 733 Mates with : 1J0 873 833

Feel free to get your own connectors if you don't like our offers, but do NOT blame us for it if you finally receive the wrong connector by accident. We can only go by reference numbers and did NOT sample every listed connector ... sorry, you had a chance.

The following table outlines the pin assignment for the efiO2Meter and both LSU 4.x versions ... please be extra careful if you make your own cable ... even we had a mistake in our 1st one :(

Please observe the pics of the connectors carefully

efiO2Meter Signal Pin LSU 4.9 Pin LSU 4.2 Pin
Virtual Gnd VM 1 yellow 2 yellow 5
Nernst Volts UN 2 black 6 black 1
Amp Current IA 3 green 5 green 2
Pump Current IP 4 red 1 red 6
Heater Neg HN 5 gray 3 gray 3
Heater Pos HP 6 white 4 white 4

LSU 4.9, LSU 4.2 Sensor and Connector Part Numbers

To our knowledge, there are 2 manufacturers for the Connectors mating the Bosch LSU4.9 and Bosch LSU4.2 Wide Band O2 Sensors. One being Bosch and the other one a company called FEP.

To add to the Mystery and Confusion over part numbers, the Bosch Connectors require Bosch Crimp Contacts and the FEP Connectors require Tyco / Amp Crimp Contacts.

As an example for the LSU4.9, the Tyco / Amp Crimp Contacts fit perfect into the FEP Housings as intended, but they fit too loose into the Bosch Housings and slip often in slightly rotated not aligning properly.

Due to the lack of having Bosch Crimp Contacts, we have not tried it the other way, but assume they will not fit at all.

Also we don't support the legacy LSU4.2 too much and did not try to obtain both types for a comparison.

To avoid typos we took pics of the labels from the bags the parts came in ...
Besides offering the parts in our shop, that's about all we can provide for our customers ...
If you want to do your own sourcing ... please have a happy browsing :)

Bosch LSU 4.9 connector parts :

EfiO2Meter FEP42121700 49.jpg

pict above FEP 42121700, LSU4.9 mating connector housing

EfiO2Meter Tyco964275-2 49.jpg

EfiO2Meter Tyco969019-2 49.jpg

pics above Tyco 964275-2 and 969019-2, LSU4.9 matching crimp contacts

EfiO2Meter boot 49.jpg

pict above RB28A0301, LSU4.9 matching Cable Boot


Bosch LSU 4.2 connector parts :

EfiO2Meter FEP42122200 42.jpg

FEP 42122200, LSU4.2 mating connector housing

EfiO2Meter Tyco964285-2 42.jpg

EfiO2Meter Tyco964281-2 42.jpg

pics above Tyco 964285-2 and 964281-2, LSU4.2 matching crimp contacts

EfiO2Meter boot 42.jpg

pict above 7807096, LSU4.2 matching Cable Boot


and here is the usual more to come :)


Note : All published design documentation is Copyright efiLabs.com and its use is without exception FOR NON COMMERCIAL PURPOSE ONLY. For commercial licenses contact efilabs.com ... try us, we're reasonable :)

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