I keep having this code come up and I need some help figuring it out. I had the car for about 5k miles before I started the kit and took it to 2 track events. The car had the GM stage 2 and (to my knowledge) no other mods. At the second track day I started getting the engine code and it blew 2 exhaust fuses. After the event I started my demo of the car (133k miles on the engine). I replace the O2 sensor, added a zzp short header, and install an air fuel gauge. I have driven about 1k miles on the kit and to it to one track day. for the most part the air/fuel reads 14.7 consistent whether WOT or on decel. However at the track it was running really lean 18+ on decel. Don't know if its because of how I drive at the track or not. anyways today I was doing some driving around town and I got the code again, but not at the track a month ago. not sure what to do.


Goblin Guru
The engine runs lean on decelleration because the fuel injectors are turned off. This is normal.
There is a bit more info here, but most of it is below.

DTC P1133


Heated oxygen sensors (HO2S) are used for fuel control and post catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content in the exhaust stream. The HO2S must reach operating temperature to provide an accurate voltage signal. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature. The powertrain control module (PCM) supplies the HO2S with a reference, or bias, voltage of about 450 mV . When the engine is first started the PCM operates in open loop, ignoring the HO2S voltage signal. Once the HO2S reaches operating temperatures and Closed Loop is achieved, the HO2S generates a voltage within a range of 0-1,000 mV that fluctuates above and below bias voltage. High HO2S voltage indicates a rich exhaust stream. Low HO2S voltage indicates a lean exhaust stream.

This diagnostic will only run once per ignition cycle. The PCM monitors the number of rich-to-lean and lean-to-rich transitions. If the PCM detects that the number of transitions were less than a specified value, DTC P1133 will set.

This diagnostic procedure supports the following DTC:
DTC P1133 HO2S Insufficient Switching Sensor 1


  • DTCs P0030, P0036, P0068, P0069, P0097, P0098, P0101, P0102, P0103, P0106, P0107, P0108, P0117, P0118, P0120, P0121, P0131, P0132, P0134, P0135, P0141, P0201, P0202, P0203, P0204, P0220, P0300, P0442, P0443, P0446, P0449, P0452, P0453, P0461, P0496, P1516, P1681, P2101, P2135, or P2176 are not set.
  • The catalyst test is not active.
  • The ECT Sensor parameter is more than 70°C (158°F) .
  • The Engine Speed parameter is between 1,000-3,500 RPM .
  • The Ignition 1 Signal parameter is between 11-18 volts .
  • The Engine Run Time parameter is more than 200 seconds .
  • The Loop Status parameter is closed.
  • The TP Indicated Angle parameter is equal to or more than 5 percent .
  • The Fuel Level Sensor parameter is more than 10 percent .
  • The MAF Sensor parameter is between 15-50 g/s .
  • DTC P1133 runs continuously when the above conditions are met for 2 seconds .

  • The PCM detects that the HO2S 1 rich-to-lean counts, or the lean-to-rich counts is less than a calibrated value.
  • DTC 1133 sets within 60 seconds when the above condition is met.

  • The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
  • The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

  • The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
  • A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
  • A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
  • Clear the MIL and the DTC with a scan tool.