2012 indmar engine oxygen sensor heater circuit causes fault

[billberry]

2012 indmar 350 monsoon bank A number 2 sensor fault spn:66021 fmi5 keeps setting off the alarm.  The fault says heater current below normal or open circuit.  Have replaced all 4 sensors.  The engine runs perfect.  Is there a way to disable that sen?  The ECU and the harness were replaced 2 years ago.

[justgary]

18 hours ago, billberry said:

2012 indmar 350 monsoon bank A number 2 sensor fault spn:66021 fmi5 keeps setting off the alarm.  The fault says heater current below normal or open circuit.  Have replaced all 4 sensors.  The engine runs perfect.  Is there a way to disable that sen?  The ECU and the harness were replaced 2 years ago.

What part of the harness was replaced?  The whole thing?

I think I would grab a meter and make sure that the sensor has a good heater.  Look for 4-8 ohms between terminals C and D.

Then I would carefully inspect the connectors at the sensor and at the ECM to make sure that a technician didn't bend the contacts while probing the harness.  You can use a small tool (I prefer a dental pick that your dentist will give to you if you ask) to gently bend the connector back to the proper shape.  This is probably the most likely cause of your problem.

Then check for 12V between terminal D and ground with the ignition on, engine off.

Then check for 0V between terminal C and battery+ with the ignition on, engine off.

If all of those pass, you'll either need a scan tool to continue or you need to watch continuously as the engine runs to catch it trying to excite the heater.  If you have two meters, you could watch the sensor on the other bank at the same time to see if they both do similar things.

[billberry]

Thanks for the reply.  I don't have the boat any longer...I sold it.  I told the buyer and I would try to help him resolve the issue.  Before he picked up the boat,  I did measure the ohms at @4 ohms.  I measured around 3-4 volts from D to one of the bolts on the engine. That sounds like a weird voltage???   I didn't check the connections to the ECM, but it sounds like it is either that as the problem, or the ECM is not functioning correctly.

[billberry]

I don't know for sure, but I believe they replaced the whole engine harness.  Thanks.

[justgary]

You could have mentioned that before I spent 20 minutes typing a useful answer... I guess I'll start out with crappy terse answers until I find out that someone really wants help. 

[Eagleboy99]

1 hour ago, justgary said:

You could have mentioned that before I spent 20 minutes typing a useful answer... I guess I'll start out with crappy terse answers until I find out that someone really wants help. 

Like Dad used to say "No good deed goes unpunished".