[405HP_Z06]

Overview
This article details a method to hijack the factory original rear oxygen sensor wiring to monitor an aftermarket wideband oxygen sensor through the ECM on a Cobb Accessport. This method disables the rear oxygen sensor emissions strategy in the ECM. The wiring diagrams are for a 2015 STI with push button start. Please reference the appropriate factory service manual for other model years to identify the correct connection points and wire colors.

Wideband Oxygen Sensor Types
Listed from the oldest technology to the newest technology -
Bosch LSU 4.2 sensor
Bosch LSU 4.9 sensor
Bosch LSU ADV sensor
4.2 vs 4.9 - Link
4.9 vs ADV - Link
Wideband discussion - Link

Data Conversion
AFR=Lambda * Stoichiometric Ratio
Lambda=AFR / Stoichiometric Ratio
Example -
Assuming stoichiometric = 14.68 and Lambda = 0.86
AFR = 14.68 * 0.86 = 12.62:1
Using the above parameters to calculate lambda
Lambda = 12.62 / 14.68 = 0.86

Wiring Supplies
Plug and play factory connectors -
The factory rear oxygen sensor and bulk head harness connectors are available from many sources. I sourced them from iWire (iWire Subaru Wiring Solutions). Using these connectors to custom build the harness that connects to the aftermarket wideband sensor and factory connectors allows for a plug and play installation.

The receptacle connector kit that connects into B19 (Rear Oxygen Sensor Receptacle A) is iWire part number CN-RE04006-0-C (Rear Oxygen Sensor Receptacle A). This is a 4-pin connector receptacle numbered 1-4.

I suggest plugging T5 for protection against damage to the connector or pins, so you can reconnect to the factory oxygen sensor in the future. This is a 4-pin connector plug numbered 1-4. The plug connector kit that connects into T5 (Rear Oxygen Sensor Plug A) is iWire part number CN-PL04006-0-C (Rear Oxygen Sensor Plug A). A note is required when ordering this part to have it assembled as a 'dummy' plug. When ordering this connector, insert "Please build with cavity plugs only (cap)" in the order notes.

Shielding the wideband controller analog positive wire -
This is not required; however, it is recommended. This wire is shielded from the factory to reduce sensor signal noise.
I used braided sleeving for shielding and grounding available from many sources. I sourced it from WireCare (WireCare.com | Your Local Cable Management Superstore!).
Shielding - Techflex FLEXO tinned copper 1/16" (Tin Copper Flexo MB Metal Braid 1/16")

Place the shield over the wire from end to end and secure with heat shrink tubing or electrical tape. The amount required will depend on the location of the wideband controller in relation to connector B19.

Extension wire -
If you need to extend the wideband controller wires, use a high quality 20 AWG wire and solder the connection points.

Wiring Harness Routes and Connections
2015 Subaru STI w/ push button start rear oxygen sensor wiring
Rear Oxygen Sensor plug in engine bay - T5 connects to B19 in the engine bay

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[405HP_Z06]

Connector B19 in the back of the engine bay on top of the transmission
Connector pin numbers are on the back of the plug or receptacle
Pin 1 - White (W) [B135 terminal 6, heater signal from ECM]
Pin 2 - Black/red(B/R) [Terminates at oxygen sensor power relay. 15A fused circuit]
Pin 3 - White (W) [B136 terminal 20, oxygen sensor signal positive to ECM, shielded wire]
Pin 4 - Yellow/red (Y/R) [B83 joint connector to B135 terminal 30, oxygen sensor signal ground]

General wideband wire connection points
12v switched power > B19 terminal 2 (B/R)
Analog positive > B19 terminal 3 (W) [shield this wire]
Analog negative > B19 terminal 4 (Y/R)
Electronics sensor ground > B19 terminal 4 (Y/R)
Heater ground > Chassis
*B19 terminal 1 is unused
[WARNING] Do NOT connect the aftermarket wideband sensor heater ground to B19 terminal 4 (Y/R)! This can damage the ECM.

Vendor specific Wideband Sensor Configuration
Connection information for specific vendor wideband systems

14Point7 Spartan 3 w/ ADV sensor
Stoich for gasoline - 14.7
Sensor type - Bosch LSU ADV or 4.9

Wire Descriptions:

Wire Connections:
Terminal 1 > B19 terminal 2 (B/R)
Terminal 2 > B19 terminal 4 (Y/R)
Terminal 3 > B19 terminal 2 (B/R)
Terminal 4 > Chassis ground
Terminal 6 > B19 terminal 3 (W) [shield this wire]
Terminal 6 shield > Chassis ground
*Terminals not listed are not used

Spartan controller values:
High Performance Linear Output settings
Bosch ADV sensor -
0v = 0.68 Lambda
5v = 1.36 Lambda

Air/Fuel ratio 5 volt settings in ECM:
Cobb Accesstuner Custom Sensor Input (Rear O2) Calibration table settings (Requires tune file to have Cobb Custom Features (CCF enabled)
Cobb Custom Features > Sensor Inputs (Custom) > Custom Sensor Input (Rear O2) Calibration
0v = 9.99 AFR
5v = 19.99 AFR

Innovate Motorsports LC-1
Stoich for gasoline - 14.7
Sensor type - Bosch LSU 4.2

Wire descriptions:
Red - A switched 12V source activated at ignition on. Suggest a minimum of a 5A fused circuit.
Blue - Heater ground. Do not ground to ECM. A good high current chassis, engine ground or battery negative terminal is the best location.
White - Sensor ground or analog output negative. This should be grounded to the same location the analog output positives are connected.
Black - Sensor calibration switch. Used to activate the calibration sequence for the sensor
Yellow - Analog output 1 or analog output positive. This is used to provide a sensor output feed to external devices. The default program emulates a narrow band oxygen sensor signal output. This can be programmed with the supplied LM Programmer software.
Brown - Analog output 2 or analog output positive. This is used to provide a sensor output feed to external devices. The default program is a 0V-5V reference signal with 0V=7.35AFR and 5V=22.39AFR. This can be programmed with the supplied LM Programmer software.
Serial Out - Used to connect to external devices and program the controller. This is the primary connection point to a computer for datalogging, analog output programming, and firmware updates. Also used to daisy chain to other Innovate Motorsport sensors and gauges.
Serial In - Used to daisy chain to other Innovate Motorsport sensors and gauges.

Wire connections:
Red > B19 terminal 2 (B/R)
Blue > Chassis ground
White > B19 terminal 4 (Y/R)
Black > Per vendor instructions
Brown (Analog 2) > B19 terminal 3 (W) [shield this wire]
Brown shield > Chassis ground
Serial Out > Computer via a serial to USB converter
*Wires not listed are not used

Air/Fuel ratio 5 volt settings in ECM:
Cobb Accesstuner Custom Sensor Input (Rear O2) Calibration table settings (Requires tune file to have Cobb Custom Features (CCF enabled)
Cobb Custom Features > Sensor Inputs (Custom) > Custom Sensor Input (Rear O2) Calibration (Data Monitoring Only)
0v = 7.35 AFR
5v = 22.39 AFR

Innovate Motorsports LC-2
Stoich for gasoline - 14.7
Sensor type - Bosch LSU 4.2 or 4.9

Wire descriptions:
Red - A switched 12V source activated at ignition on. Suggest a minimum of a 5A fused circuit.
Black - Do not ground to ECM. A good high current chassis, engine ground or battery negative terminal is the best location.
Black - Sensor calibration switch. Used to activate the calibration sequence for the sensor
Brown - Analog output 1 or analog output positive. This is used to provide a sensor output feed to external devices. The default program emulates a narrow band oxygen sensor signal output. This can be programmed with the supplied LM Programmer software.
Yellow - Analog output 2 or analog output positive. This is used to provide a sensor output feed to external devices. The default program is a 0V-5V reference signal with 0V=7.35AFR and 5V=22.39AFR. This can be programmed with the supplied LM Programmer software.
Serial Out - Used to connect to external devices and program the controller. This is the primary connection point to a computer for datalogging, analog output programming, and firmware updates. Also used to daisy chain to other Innovate Motorsport sensors and gauges.
Serial In - Used to daisy chain to other Innovate Motorsport sensors and gauges.

Wire connections:
Red > B19 terminal 2 (B/R)
Black > Chassis, engine ground or battery negative terminal
Yellow (Analog 2) > B19 terminal 3 (W) [shield this wire]
Yellow shield > Chassis ground
Serial Out > Computer via a serial to USB converter
*Wires not listed are not used

Air/Fuel ratio 5 volt settings in ECM:
Cobb Accesstuner Custom Sensor Input (Rear O2) Calibration table settings (Requires tune file to have Cobb Custom Features (CCF enabled)
Cobb Custom Features > Sensor Inputs (Custom) > Custom Sensor Input (Rear O2) Calibration (Data Monitoring Only)
0v = 7.35 AFR
5v = 22.39 AFR

AEM 30-0310
Stoich for gasoline - 14.65
Sensor type - Bosch LSU 4.9

Wire Descriptions:
Red - A switched 12V source activated at ignition on. Suggest a minimum of a 5A fused circuit.
Black - Do not ground to ECM. A good high current chassis, engine ground or battery negative terminal is the best location.
Blue - The serial data stream is suitable for output to third party devices such as data loggers, PCs, or reflashed ECUs. The X-Series UEGO serial data stream is designed to match AEM's legacy 30-4100/30-4110 UEGO Digital Gauge for backwards compatibility.
White - Analog output signal positive wire connected to the positive of the analog input of a logging device or ECM
Brown - Analog output signal negative wire connected to the negative of the analog input of a logging device or ECM
Green/Black - AEMnet output signal positive or CAN High is suitable for output to AEM devices such as the AQ-1 data logger or Infinity ECU.
White/Black - AEMnet output signal negative or CAN Low is suitable for output to AEM devices such as the AQ-1 data logger or Infinity ECU.

Wire Connections:
Red > B19 terminal 2 (B/R)
Black > Chassis, engine ground or battery negative terminal
White > B19 terminal 3 (W) [shield this wire]
Brown > B19 terminal 4 (Y/R)
White Shield > Chassis, engine ground or battery negative terminal
*Wires not listed are not used

Air/Fuel ratio 5 volt settings in ECM:
Cobb Accesstuner Custom Sensor Input (Rear O2) Calibration table settings (Requires tune file to have Cobb Custom Features (CCF enabled)
Cobb Custom Features > Sensor Inputs (Custom) > Custom Sensor Input (Rear O2) Calibration (Data Monitoring Only)
0.5v =8.5 AFR
4.5v = 18 AFR

Continued in next post...

 

[405HP_Z06]

AEM 30-0300
See AEM 30-0310 for configuration and wiring. Gauge output wiring is shown below.

ECM Software Parameter Modification
Rear Oxygen Sensor Fueling Targets and Limits
The rear oxygen sensor plays a role in close loop air/fuel targets and learning in the factory ECM. These limits and compensations must be eliminated to maintain proper closed loop operation with the rear oxygen sensor signal wiring hijacked for wideband sensor monitoring.

Catalyst efficiency and diagnostic trouble codes
The ECM monitors catalyst efficiency using oxygen sensor values. The catalyst system efficiency diagnostic trouble code (DTC) must be disabled to prevent a check engine light condition. Access to Cobb Accesstuner or a local tuner is required for the ECM adjustments to enable this modification.

In Cobb AccessTuner -
Fuel Tables > Closed Loop Target >
A/F Correction #3 Limits (Max/Min)
Stock -
Max 50
Min -50
Modified
Max 0
Min 0

A/F Learning #3 Limits (Max/Min)
Stock
Max 50
Min -50
Modified
Max 0
Min 0

Closed Loop Fueling Target Compensation (Rear O2) Limits (Max)
Stock
Max 50
Modified
Max 0

Closed Loop Fueling Target Compensation (Rear O2) Limits (Min)
Stock
Min -50
Modified
Min 0

In Cobb Accesstuner -
Edit > Advanced Parameters... (F11)
DTCs (Base) > P0420 Catalyst System Efficiency Below Threshold
Uncheck this value

Cobb Accessport Configuration
Configure the Accessport to monitor the following parameters. Sns Volts Rear O2 is more precise but may be a little harder to read because no smoothing is applied to the output.

Sensor Input Monitor Only REAR O2 (Sns Only Rear O2) [EJ 2.5L CFF]
This value is determined from the Rear O2 voltage input and the Custom Sensor Input (Rear O2) Calibration... table with smoothing applied (Custom Sensor Input (Rear O2) Smoothing Factor... table).

or

Sensor Input Voltage REAR O2 (Sns Volts Rear O2) [EJ 2.5L CFF]
The raw voltage input to the ECU from the Rear O2 sensor circuit.

 

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