O2 Sensor

[CRJEEPER]

Hi all,

Have a '97 Wrangler, 4 cylinder, 5 spd. Getting poor gas mileage (like 7 mpg) and the Jeep is idling rough. It threw a code indicating that the O2 sensor's signal is not changing (it's stuck at one reading). Got these codes:

21: Upstream oxygen sensor response slower than minimum required switching frequency.

Upstream oxygen sensor heating element circuit malfunction.

Downstream oxygen sensor heating element circuit malfunction.

Downstream oxygen sensor input voltage maintained above the normal operating range.

Oxygen sensor voltage too low, tested after cold start. (Upstream or Downstream)

Left oxygen sensor input voltage maintained above the normal operating temperature.

Anyone messed with the O2 sensors lately? If so, could someone provide some help? Thanks.

[OhioYJ]

A real time scanner would be a big help here, the first question would be are the O2 sensors both getting voltage from the ECM?

The low voltage is indicating a lean mixture, so your ECM is dumping fuel into the motor cause it thinks it lean, hence your bad gas mileage and rough idle.

Make sure your O2 sensor harnesses haven't been burnt by the exhuast pipe, and make sure the connections aren't all corroded. Then its either time to break out the multi-meter and checking voltages, or find a real time scanner and see what the ECM is getting back from the O2 sensors.

[2001YellowTJ]

i was getting a high voltage o2 sensor reading and it ended up being the battery. It was the original battery and it needed to be replaced.