Test TC-9A - O2S Stays Below Center (Lean) (DTC 51)

WARNING: This page is about a different car, the 1994 Plymouth Acclaim and 1994 Dodge Spirit. However, it is still accessible from the selected car via links, so may be relevant.

NOTE: For circuit and connector terminal identification, see CONNECTOR IDENTIFICATION DIRECTORY TABLE . For wiring diagrams, see WIRING DIAGRAMS .

Start engine and apply parking brake. Using DRB, set engine speed to 1500 RPM. Using DRB, read oxygen sensor voltage. If oxygen sensor voltage is not always less than .5 volt, condition required to set trouble code is not present at this time. Go to next step. If oxygen sensor voltage is always less than .5 volt, go to step 3).
The O2S STAYS BELOW CENTER (LEAN) trouble code sets if oxygen sensor output voltage stays less than .5 volt for at least 8 minutes. Possible causes are: low fuel pressure, vacuum leak, other engine sensor calibration failures, ignition system failure, oxygen sensor failure or mechanical engine failure. Go to TEST NTC-1A .
Using DRB, check if oxygen sensor voltage is always at zero volts. If oxygen sensor voltage is always zero volts, go to step 5). If oxygen sensor voltage is not always zero volts, check oxygen sensor connector for excessive dirt and/or grease build-up. Closely check oxygen sensor connector Black/Dark Green wire for tracking to oxygen sensor connector Black/Tan wire and Black/Light Blue wire.
If excessive dirt and/or grease build-up is present, clean oxygen sensor connector as necessary. Perform TEST VER-2 . If excessive dirt and/or grease build-up is not present, a condition causing engine to run lean is indicated. Go to TEST NTC-1A.
Using DRB, stop all actuation of vehicle components. Turn ignition on with engine off. Disconnect oxygen sensor connector. Using DRB, read oxygen sensor voltage. If oxygen sensor voltage is always .5 volt, replace oxygen sensor. Perform TEST VER-2.
If oxygen sensor voltage is not always .5 volt, turn ignition off. Disconnect Powertrain Control Module (PCM) connector. Put DRB in ohmmeter mode. Using DRB, check resistance of Black/Dark Green wire (Dark Green/White wire on Dakota) on oxygen sensor connector harness side.
If resistance is less than 5 ohms, repair short to ground in Black/Dark Green wire (Dark Green/White wire on Dakota). Perform TEST VER-2. If resistance is more than 5 ohms, replace PCM. Perform TEST VER-2.