2004 Chrysler Town and Country O2 Heater circiuits

For this particular vehicle there is also a known problem with many ECU firmware versions where neither replacing the O2 sensor nor clearing DTC codes, nor sucessful drive cycles can clear this error once it is set. It is true that the original factory oxygen sensors have a very low resistance when cold (4-8 ohms) while most replacement sensors are higher (10-20 ohms). Installing a currently available "genuine MOPAR" oxygen sensor (OEM Densu) or any other sensor with any chosen cold resistance will not resolve the problem. The code will always return after at least one drive cycle long enough to count followed an idle cycle long enough to cool the engine, followed by a drive cycle. The only resolution is to have a dealer reflash the engine firmware with a corrected version. There is a Chrysler Service Bulletin, however Chrysler is not offering this as a recall item.

With the engine off, disconnect the O2 sensor and check the O2 heater resistance is 20 ohms or less. Reconnect the )2 sensor leads and probe the heater leads with the engine running and verify that the O2 sensor heater is powered, and the ground lead is reasonably grounded. If these basic checks are good, the problem is likely to be the ECU firmware. Some dealerships insist on installing MOPAR 02 sensor(s) for several hundred dollars as a first step. Some dealerships charge $100 to $150 to diagnose and update the ECU firmware. Some dealerships accept the 3rd party diagnosis and the Service Bulletin and perform this brief (10 minute) chore for a fee more likely to encourage your continued patronage.

I should also add that the headlamp failure is unlikely to be related. The circuits do not share a ground as originally configured.

It is concievable, but unlikely that the headlamp failure caused a brief circuit disturbance precisely during the 02 heater functionality test at the beginning of a drive cycle, triggering a false error that was then incorrectly retained by the known ECU firware bug. The more elaborate 02 heater test during the off cycle is described as initiating more than 20 minutes after the engine shuts off, a time when the headlamp is likely to have been on.

Is there any chance you know the bulletin number, or have a link, to the O2 sensor / ECU firmware issue? Our Chrysler service center is claiming that there's no such thing as replacing the firmware.

(We have a 2004 T&C, which had the O2 sensor replaced because the code said that was the problem. Our mechanic says the new sensor is fine, and that the dealer needs to update the firmware to handle the new sensors.)