Hi, everyone. Just signed up. I was hoping someone might lead me in the right direction with a P1133 DTC my friend'* been getting on her Regal.

After doing some digging, it seems a major cause of the code is a malfunctioning O2. Although the existing sensor on the car was only 6 months old, I replaced it again (with one from a different manufacturer). I erased the code but it came back within a day.

I don't know if this is related, but the code seemed to pop up not long after we had the MAF replaced. There also have been some driveabilty issues since that time, specifically being on occasion during startup the car will stall out or otherwise won't rev properly (given accelerator pedal position) within the first 10 seconds or so of the engine running.

Would anyone have a hunch as to what the problem might be? The scanner I have gives me live data and all that good stuff if it;* helpful.

Many thanks.

A few things.

First off, the recommended choice of oxygen sensor is ACDelco or Denso. Bosch is generally avoided in these parts.

I had to go look up the code meaning:
P1133 BUICK - HO2S Insufficient Switching Bank 1 Sensor 1

It looks like this code was meant to weed out aging and lazy oxygen sensors. From what I gather, the computer is expecting the sensor reading to be constantly fluctuating between 'rich' and 'lean'. Each time it switches (or 'crosses' depending on who you talk to), the computer reacts to keep the fuel mixture on point. What I would be doing is scanning live o2 data to see what the sensor is doing. It'* possible it may be hanging rich or lean, but not enough to trip the associated code. This would be obvious when looking at live data, because I would expect the o2 values to be constantly and rapidly changing, but never really crossing the switch threshold.

It could be related to the MAF, especially if the MAF is not correctly reading the air volume coming in. MAF Sensors (especially aftermarket replacements) have also been known to be fairly sketchy, especially if a MAF screen was removed. Most have the best luck with a known good salvaged OEM unit.

There are a number of other possibilities as well, but they are dependent on the o2 data behaviors, which can be expanded upon once we find out exactly what it is doing.

What Rjolly is talking about is "crosscounts"......that involves the mythical 0.455 volt line......every time the voltage goes above or below the mason dixon line, you create a cross count....the PCM looks for a minimum finite number of crosscounts in a specific time frame.....too low and the code is set....

I don't know if your scan tool is capable of plotting data, but even my cheap $20 Bluetooth interface scanner can plot a graph on my smartphone......as Rjolly stated, you want to see a quick changing waveform(sinusoidal), above and below 0.455 DC volts......if you don't, disconnect the MAF, and if you get a normal waveform, the problem is your MAF.....if still the same, be looking for a vac leak, if the waveform stays low, or leaking injector, f/p regulator, dirty airfilter, etc., if it stays high...

Thanks very much for the speedy replies, guys.

I gonna hop over to the salvage yard on Sat and pick up another MAF, I think. The one that'* in there is from AutoZone.

I do believe my autel AL519 has graphing capability. If the code comes back after I replace that sensor, I'll follow your instructions on getting the zero crossing info. I'll also check my paperwork to see what brands of o2'* we used...

Have a great day and thanks again

Just wanted to update you all on my progress (or lack thereof) of the regal,,,

I went over to the scrapyard but found they'd only sell me the whole throttle body (with the sensor on it). They they wanted a lot of $ for it and since I didn't really know if I was getting a true non-reman MAF anyway, I ended up buying a new one again, this time from advance.

Before I installed it, I rescanned the computer and noticed the original P1113 was gone, now replaced with P0135 and P0141- O2 heater malfunction of upstream/downstream heater element, respectively. I checked upstream O2 for power and noticed no +12V present at terminal D. Checked #29 fuse under the hood and noticed it was blown. I replaced fuse, found +12 present at the terminal, installed MAF, cleared codes, and started driving car.

Been driving it for a bit and have found pending code of P0141. I checked downstream O2 on terminal C and D (harness side) for ground, +12 and C and D again (sensor side) to test heater element resistance. Ground and +12 checked out and element resistance was 5.1 ohms, which seems to be in acceptable limits.

Since the I replaced the MAF, the car has been running better at startup. No more stalling out or throttling problems like before. I'm not sure what the pending P0141 is about, though. Guess I'll keep driving the car and see if it turns into an actual DTC.

Well, 1133 is back again.

I was able to look at the graph of the O2 and at idle it was all over the place. I increased rpms to ~1500 and noticed the frequency increased and the waveform improved looking more sinusoidal, but still not very good. The low voltage value did not always dip as low as compared to some other periods. Unplugging the MAF at idle still resulted in an erratic readout but at 1500 it actually looked quite good, consistently hitting the same high and low values and looking mostly sinusoidal.

I tested fuel pressure at the test port by the regulator and got 40psi. Pressure increased momentarily when I revved engine to a steady 3krpm, but settled back to 40 quickly.

Air filter was changed. I checked for vac leaks and changed a couple of hoses that looked suspect. Not 100% sure I caught all the vac ports coming off the motor. I counted 2- one in the back of engine and one in the front. I sprayed carb cleaner around the intake manifold but didn't notice any change in idle.