O2 Sensor Replacement Fixed Rough Idle & Limp Mode of E90 M3 [ENG SUB]

Malfunction of an oxygen (O2) sensor BEFORE the catalyzer caused BMW E90 M3 rough idle and limp mode. The replacement of the O2 sensors before cat and adaptation reset resolved the problem.

[Errata] The “thread glue” I mentioned is actually an anti-seize lubricant.

The cold start process of stock E9x M3 may generate misfire codes. See this video “Cold Start Delete DIT Fixed Rough Idle and Misfire Codes”:    • BMW E90 M3 Cold Start Delete Fixed Ro...   for more info.

A bad O2 sensor before cat stops the engine control unit (DME) from calculating correct air to fuel mixture. The engine will end up in poor combustion, misfire, vibration and eventually limp mode (or limp home mode, BMW’s protection for the engine.) Here I changed the O2 sensors before cat on both banks of the S65B40O V8 engine to ensure the DME gets an accurate signal. After the replacement, adaptation reset of the O2 sensors is necessary. And the replacement successfully fixed the problems mentioned above.

**Codes for O2 sensor before cat. on bank 1(they came randomly)**
2724 DME: Oxygen sensor, signal before cat., bank 1
2726 DME: Oxygen sensor, plausibility before cat., bank 1
2728 DME: Oxygen sensor, coast-mode diagnosis before cat., bank 1
2742 DME: Oxygen sensor heater resistance diagnosis before cat. converter, bank 1
2748 DME: Oxygen sensor before cat., evaluation module in control module, bank 1
277C DME: Oxygen sensor trim control diagnosis, bank 1

**Codes accompanied with limp mode I had**
2B35 DME: Misfire with cutoff, cyl. 1
2B36 DME: Misfire with cutoff, cyl. 2
2B37 DME: Misfire with cutoff, cyl. 3
2B38 DME: Misfire with cutoff, cyl. 4
2B41 DME: Misfire with cutout, several cylinders
2B42 DME: Misfire impairing exhaust emission, cyl. 1
2B43 DME: Misfire impairing exhaust emission, cyl. 2
2B44 DME: Misfire impairing exhaust emission, cyl. 3
2B45 DME: Misfire impairing exhaust emission, cyl. 4
2B4E DME: Misfire impairing exhaust emission, several cylinders

**Parts Required**
Oxygen sensor BEFORE catalyzer X2
BMW 11 78 7 537 984
Bosch LS 17038 / 0 258 017 038

**Tools Required**
8 mm hex socket (trims)
10 mm hex socket (trims)
17 mm hex socket (reinforcement strut/plate bolts)
torque wrench with angle (56 Nm + 90°)
22 mm open hex spanner (O2 sensor)
22 mm open hex torque spanner (25-50Nm)

**Tightening torque spec**
O2 sensor before catalyzer 50 Nm (OE exhaust)
after cat 25 Nm (OE exhaust)
Bolts on reinforcement strut/plat 56 Nm + 90° (replace blots)

**Sections**
0:00 Opening
0:27 Intro
Disassembly
4:33 Removing transmission cover
6:03 Removing underhood shield
7:10 Removing reinforcement strut
7:53 Removing O2 sensors
9:23 Close look at O2 sensors
Assembly
10:22 Installing O2 sensors
14:47 Adaptation reset
16:07 Installing reinforcement strut
18:28 Installing underhood shield
18:52 Installing transmission cover
20:19 Test run
Summary
20:36 Closing remarks

Camera: Jing-Ru

Music: Ventura by Morgan Taylor
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