SPN: 66019 & 66020 (Both "FMI:8 Abnormal Frequency or Pulse Width")

[kevinshields]

I am seeing the following two Diagnostic Trouble Codes:

• SPN:66019 FMI:8 Abnormal Frequency or Pulse Width
• SPN:66020 FMI:8 Abnormal Frequency or Pulse Width

Thanks to a few other helpful posts in this forum I was able to look these codes up in the Indmar Service and Diagnostic Manual.  I believe the pages of interest start at 9-186.  The manual directs attention as follows:

• SPN 66019 FMI 8: Oxygen Sensor Bank A Sensor 1 Heater Abnormal Frequency or Pulse Width
• SPN 66020 FMI 8: Oxygen Sensor Bank B Sensor 1 Heater Abnormal Frequency or Pulse Width

As I understand it this engine has four HO2S sensors - two each per exhaust side (per "Bank").  One sensor is placed before, the other after, the catalytic converter.

Question 1: Am I correct that Sensor 1 is before the catalytic converter?

For 02 sensor issue, I would typically swap sensors between banks to see whether the problem follows the sensor.  However in this case I am getting errors on both sensors... so swapping them seems like a waste of time.

If I understand these systems correctly it is quite likely I am chasing one of three faulty components (please ack if I am mistaken):

1. Wiring (9-188: Circuit/System Testing)
2. Sensor (9-44: H02S Replacement)
3. Engine Control Module (9-226: ECM Replacement)

Question 2: If I swapped ECMs will I need to do a bunch of programming or can I reasonably assume it is "plug and play"?

At 9-187 the manual directs that "Conditions for Setting the SPN" for "66019 and 66020 FMI 8" are as follows: "The ECM detects that the heater control duty cycle is greater than 90 percent for greater than 160 seconds."  I haven't a clue what these words are intended to communicate.  ;-)

Question: 3: Is this saying it is possible there is an issue with the engine that is causing these faults?  (I am presently assuming this is not a mechanical issue - I presume that if the O2 sensor detected an issue it would spit out the code telling me I need to check for an exhaust lead or something... ?)

Question 4: Any advice on the next steps?

Many thanks in advance!

[csleaver]

All four of the O2 sensors are the same on that engine, so you could still swap the pre cat and post cat O2 sensors for testing.  The most common issue is coking, or exhaust soot coating the sensor.  This is caused by running heavily loaded below 4000 RPM.  Running the boat unloaded above 4000 RPM for 10 mimutes can sometimes clean the soot off of the sensors.  I would consider an ECM swap a last resort for diagnosing the problem.

Edited May 31, 2022 by csleaver

[kevinshields]

16 hours ago, csleaver said:

The most common issue is coking, or exhaust soot coating the sensor.  This is caused by running heavily loaded below 4000 RPM.  Running the boat unloaded above 4000 RPM for 10 mimutes can sometimes clean the soot off of the sensors.  I would consider an ECM swap a last resort for diagnosing the problem.

Holy smokes that is a super helpful response, many thanks for your reply!

I can totally believe this is a function of running fully loaded at low RPM.  The boat was fine most of the day until we had filled with gas and did a bit more surfing... so we gained a ton of fuel weight in addition to the seven pre-adults and extra ballast bags.

I will go run it unloaded to see if that clears the soot.  Thanks again!!!!

Quote

All four of the O2 sensors are the same on that engine, so you could still swap the pre cat and post cat O2 sensors for testing.

BTW do I understand it correctly that all four of the 02 sensors are the same part number?  Thus in theory I could swap both across banks and also between positions? (I won't bother with this until after running it hot for a while to see whether I can clean the soot).

Edited May 31, 2022 by kevinshields

[csleaver]

Indmar used the same narrow band O2 sensors for the pre and post cat on all GM engines from 2009 to 2015.

[scottgordon]

What side of engine is the right side?  Right Looking at the engine or Right based on the boat going forward?

[justgary]

5 hours ago, scottgordon said:

What side of engine is the right side?  Right Looking at the engine or Right based on the boat going forward?

Pull a sensor wire and find out!

[cartercc]

@kevinshields I have been fighting this issue for two years now. With my marina looking at it as well as Texas Malibu. Changed all o2 sensors amongs other attempts at the fix. It keeps coming back? Did you ever get it fixed? Was it just cleaning some sensors?