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Guide Rear O2 delete
For Jeep and Dodge PCMs (JTEC and JTEC+) whose calibration has the rear (downstream) oxygen sensor options in CalibraX. The guide is a template: the tables are always the same, and what changes with the engine is which rear sensors your calibration has.
Use and responsibility. Removing the rear O2 sensor and switching off its monitors is meant for off-road and competition vehicles. On a road vehicle it can break emissions rules in your country, and the vehicle will not pass an inspection (the readiness monitors will show as not complete). You are responsible for what you do with your vehicle.
- Read the PCM and keep the original
.binsomewhere safe. To undo everything you write that file back. - Open the file in CalibraX and check that its calibration is in the Supported vehicles list.
- Save the project under a new name before the first change.
Open General › General - Configuration. The four oxygen sensor check boxes are named like this:
| Check box | Sensor |
|---|---|
| O2 Sensor 1/1 Installed (Bank 1, Upstream) | front, bank 1 |
| O2 Sensor 1/2 Installed (Bank 1, Downstream) | rear, bank 1 |
| O2 Sensor 2/1 Installed (Bank 2, Upstream) | front, bank 2 |
| O2 Sensor 2/2 Installed (Bank 2, Downstream) | rear, bank 2 |
Look at which of the two rear boxes are checked in your file. Those are the sensors you remove. A rear box that is already unchecked needs nothing, and neither do its tests (Step 4). Never uncheck a front sensor.
Typical stock files of the 1997 family (this varies by calibration, trust what your file shows):
| Engine | Rear sensors checked | What you do |
|---|---|---|
| 2.5L 4 cyl, 3.9L V6, 4.0L 6 cyl | usually 1/2 only | Remove 1/2 |
| 5.2L and 5.9L V8 | usually 1/2 only; some files have both | Remove the rear ones that are checked |
| 8.0L V10 | both (1/2 and 2/2), or none | Remove the rear ones that are checked |
| Diesel (Cummins) | none | Not applicable |
In General › General - Configuration, uncheck the rear box (or boxes) you found.
In Diagnostics › Diagnostics - Monitors:
| Item | Codes | Change |
|---|---|---|
| Downstream O2 heater monitor | P0141 (bank 1), P0161 (bank 2) | Off |
| Downstream O2 sensor monitor | P0139, P0159 | Off (many calibrations have it off already) |
| Catalyst monitor | catalyst response codes | Off |
| Catalyst efficiency monitor (EWMA) | P0420, P0432 | Off |
Without the rear sensor the catalyst monitors have nothing to compare against and would set a code.
In Diagnostics › Diagnostics - Rationality, for each rear sensor you removed:
| Sensor | Low input | High input |
|---|---|---|
| O2 1/2 (bank 1 rear) | O2 1/2 low input (P0137) | O2 1/2 high input (P0138) |
| O2 2/2 (bank 2 rear) | O2 2/2 low input (P0157) | O2 2/2 high input (P0158) |
Leave the tests of the front sensors (1/1 and 2/1) as they are. These tests are also part of the limp-in protection: switching one off removes that protection for that sensor.
In the JTEC+ calibrations (1999-2005) the list is longer and the numbers differ; look for the items by their P-code in the name.
Nothing to change in Fuel › Fuel - Downstream O2. With the sensor declared absent the PCM stops using it and runs the front sensor with its own goal tables.
- Save, let CalibraX correct the checksum, and write the file to the PCM.
- Disconnect the battery for a few minutes. The PCM keeps a correction it learned while the rear sensor worked and keeps applying it to the front sensor until the memory is cleared.
- Reconnect, clear the codes and start the engine.
- In the Logger, watch the front O2 sensor switching and the fuel trims, cold and at operating temperature. The trims should settle near zero.
- Read the trouble codes: P0137, P0138, P0139, P0141 and P0420 (and the bank 2 ones if you removed that sensor) should not come back.
- If the check engine light comes on with a front sensor or fuel code, undo the last change and check the front sensor and the exhaust for leaks.
Write the original .bin you saved and disconnect the battery again.
| Family | Status |
|---|---|
| JTEC 1997 | |
| JTEC 1998 | |
| JTEC+ 1999-2005 |