This is because cold (or just warm) O2 sensors don't work very well, and they take a little while to get good and hot. When you fire the beast up, whether the engine is stone cold or fully warmed up, the PCM starts out in open loop. Learning disabled means that the PCM is ignoring the O2 sensors, which is the same as saying that the PCM is using a version of open loop fuel control. In PE mode the scan tool may report that the PCM is in closed loop, but it should also report that learning is disabled. But even after this switch, if you lean on the throttle hard enough, the PCM will switch to power enrichment (PE) mode, which is another form of open loop. Once the PCM decides that conditions are right, it switches to closed loop fuel control, which is described below the open loop discussion. This version of open loop is described in the next section. Right after a cold or hot start, a scan tool will report that the PCM is using open loop fuel control.
Note that there are 2 kinds of open loop. O2 sensor correction is not used in open loop. The PCM injector pulsewidth calculation also uses the INT and BLM correction factors based on O2 sensor feedback when it is in closed loop. I would be concerned if it doesn't switch between open and closed loop modes.Įxecutive summary: The PCM controls the fuel injectors by using signals from the engine sensors, like MAP, MAF, RPM, ECT, and others to pick out the right value from the right lookup table to use in the fuel injector pulsewidth calculation. It should operate in closed loop when in idle after proper warm up and at cruising speeds. It is supposed to switch depending on driving conditions and engine parameters.Īcceleration and idle until warm up to around 145 degrees is classified as open loop operation. An odb-ii emissions system operates in two modes.open and closed loop for fuel control.