Magazine for the auto service professional
Issue link: http://asp.epubxp.com/i/392413
39 | September/October 2014 Circle 122 on Reader Service Card customer she needs a PCM, it is wise to fnd any other evidence of a module issue. One way to do this is to look at the PIDs and see if there is something that does not make sense. Because there was a system lean DTC, the O 2 sensor PIDs were looked at frst. Since a reading of about 3.3V is normal for an air-fuel ratio sensor and the vehicle was in that ballpark, it was wise to move on to the rear oxygen sensor. The readings were frozen at 15 mV (see Figure 8). This was obviously abnormal. There wasn't an exhaust leak, so it was decided to back- probe the rear oxygen sensor. It gave us good readings. Why was the PCM not pick- ing it up? At this point, the connector to the rear oxygen sensor was disconnected and wiring to the PCM was checked. The wiring checked out, but interestingly enough after plugging in the sensor the PCM started picking up rear O 2 data (see Figure 9). Since there was not any corrosion or any debris on the connector, it did not seem wise to just consider the vehicle "fxed." After all, the oxygen sensor connector did not disconnect itself or have any corrosion on it. However, the battery sure had corro- sion! (See Figure 10.) The battery terminals were cleaned, a soft reset performed, and idle was relearned. On Toyotas, to relearn idle the vehicle has to be test driven a few miles. There have not been any problems with the vehicle since. ● Connections Figure 10: A corroded battery can sometimes create weird electrical issues. Always do the basics before moving forward.