A code 3 on the diagnostic module (Pin 19 or push button LED):
Lambda control inoperative Test LH-SFI unit

A code 3 on the diagnostic module does not necessarily mean it is the O2 sensor. A code 2 would.

You need to build the code reader an check Pin 4 for codes, this will narrow down the issue.

Codes for Pin 19 (the same as the push button LED):
1 No Faults in System -
2 Heated oxygen sensor inoperative Test LH-SFI unit
3 Lambda control inoperative Test LH-SFI unit
4 Air injection inoperative Test LH-SFI unit
5 Exhaust gas recirculation inoperative Test LH-SFI unit
6 Idle speed control inoperative Test electronic accelerator
7 Ignition system defective Test distributor igntion system
8 Engine coolant temperature sensor, open/short Test LH-SFI unit
9 Intake air temperature sensor, open/short Test LH-SFI unit
10 Voltage at mass air flow sensor too high/low Test LH-SFI unit
11 TN-signal (rpm) at LH-SFI control module (N3/1) defective Test LH-SFI unit
12 Heated oxygen sensor heater, open/short circuit Test LH-SFI unit
13 Camshaft position sensor signal of ignition control module (N1/3) defective Test LH-SFI unit
14 Intake manifold pressure at start in N1/3 too low/high Test LH-SFI unit
15 Wide open throttle information defective Test LH-SFI unit
16 Closed throttle position information defective Test electronic accelerator
17 Data exchange malfunction between individual control modules Test DM Step: 7.0
18 Adjustable camshaft timing solenoid, open/short circuit Test LH-SFI unit
19 Fuel injectors open/short or self-adaptation in LH-SFI control module (N3/1) at limit Test LH-SFI unit and reset adaptation to mean value
20 Speed signal not present Test electronic accelerator
21 Purge switchover valve, open/short circuit Test LH-SFI unit
22 Camshaft position sensor signal defective Test distributor system
23 Intake manifold pressure in N1/3 with engine running too high/low Vacuum supply to N1/3; Test distributor ignition system
24 Start ring gear segments and/or crankshaft position sensor defective Test distributor system
25 Knock sensors or ignition control module defective Test distributor system
26 Upshift delay 1 to 2 (model 123.034) , 2 to 3 (all models) Test LH-SFI unit
27 Engine coolant temperature sensor deviation between sensor ckt 1 and sensor ckt 2 Test LH-SFI unit
28 Engine coolant temperature sensor (coolant temperature change monitor Test LH-SFI unit

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