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2008 BF150 - Check engine light is on, no unusual beeps, no saved codes

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Flot

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Troubleshooting a new to me BF150

Engine is running great on the hose, but the check engine light is on. No unusual beeps.

I performed the code read procedure by jumping the red plug -no flashes - but it gives me a confirmation beep when I reset (5 pushes on the safety lanyard trigger) which makes me think I'm doing it right. Despite that the check engine light remains on.

What would trigger a check engine with no codes and not be able to clear it?
 
Update: I was able to simulate a different check engine light by unplugging the O2 sensor. This code clearly flashed when doing diagnostics, and I was able to reset THAT false code using the lanyard procedure.

However, the check engine light continued to stay on for my original problem.
 
Do you have the 4-light console? (Oil pressure (green), overheat (red), alternator (red) or MIL (PGM-FI - i.e. check engine, red)? If so, are you sure you are seeing the MIL (engine fault) light, or possibly an alternator light, or overheat light?
 
I should have said above, I was able to simulate a different check engine code. Same light. :)

I do have the 4 light console (which I bought separately from the motor) and initially I had some doubts about whether it was wired properly - but yes, the light literally says 'check' and when I disconnected the O2 sensor, I was able to read the fault codes the light blinking, and reset the O2 fault. So that confirms I'm looking at the right light and it is connected properly and working as designed. Despite the reset, the O2 code went away, but the check engine light stayed on.

I ordered a code scanner but am not confident that'll tell the story either. In the service manual there are a handful of things that it says could cause a check engine light with no codes, but none of them seem especially plausible or helpful for diagnosing. (things like no voltage on the ECU wire, which I presume would also keep the engine from running) I saw a number of similar threads where people said to check water in fuel but that seems like it would also set a constant alarm.
 
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I cannot think of any situation where you get beeps on the alarm (saying that it is working) and a check engine light, but no codes.

Perhaps Ian in Australia has some thoughts on that.
 
How many Hours on the engine? If you run on muffs with a splitter also going to flush line you will get sufficient cooling water to keep it from overheating when testing. Could be heater line portion of o2 sensor has gone bad. A/F sensor abnormal current will make the MIL light stay on. Do voltage checks on A/F sensor and A/F sensor relay. If it passes voltage, do Ohms test 2-3 ohms on the A/F sensor heater lines #3 black and #4 black wires. If below 2 ohms replace A/F sensor.
 
Perfect, thanks for that list, will check. I believe motor has ~250 hours on it based on previous info but have not plugged it in. I can run on muffs below ~1500 rpm no problem, higher than that and it'll throw an overheat alarm pretty quickly. I did all the routine service last year when I picked the motor up, just finally got it rigged. Previous owner is a friend who ran the motor for a few months, but I don't think he had the full gauge package and may not have had warning lights hooked up.

Will check the list above!
 
HonDan said:
How many Hours on the engine? If you run on muffs with a splitter also going to flush line you will get sufficient cooling water to keep it from overheating when testing. Could be heater line portion of o2 sensor has gone bad. A/F sensor abnormal current will make the MIL light stay on. Do voltage checks on A/F sensor and A/F sensor relay. If it passes voltage, do Ohms test 2-3 ohms on the A/F sensor heater lines #3 black and #4 black wires. If below 2 ohms replace A/F sensor.
Click to expand...

@HonDan I got a healtech scanner and threw it on quickly - I don't see anything particularly out of whack running at idle or low RPM, and no codes read - will check the above this weekend.

I took a few screenshots between 800-1200 rpm (only ran it for a minute or two on the hose) and I did see this:

Heated Oxygen Sensor Control: - ON sometimes, OFF sometimes
however
Heated Oxygen Sensor voltage 0.000 V at all times

Is that enough evidence to replace the O2 sensor? Motor doesn't need to be at a certain RPM or warmed up does it?

Motor only has ~170 hours but obviously that is a LOT of sitting around not running for a 2008. But it had to be stored indoors most of its life, because it looks pristine.
 
Have you checked the fuses #1 and #5? Service manual A/F sensor heater troubleshooting Page 5-89 starts with resetting the ECM does your healthtech scanner have the ability to do that? If you check voltage with a multimeter at the a/F sensor harness side the green and white top left #1 of the A/F sensor socket I get 1.8v and on the right #2 yellow and red I get 2.1v, so there are two seperate voltages going to the A/F sensor. There is no mention in service manual if one of those two shuts voltage supply to the heater circuit at a certain temp or amount of time. It says run engine at 3000rpm for 5 minutes. seems a bit high to do on a hose. Nor it doesn't say if heater circuit turns off certain number of seconds and what voltage should be seen after this point.
If no volts at the socket to either #1 or #2 then the A/F relay is likely the problem and it is In the fuse box item #8 can find these used on ebay for $20 38543-ZY6-003

I have 2.1 Ohms resistance on the A/F sensor itself wires #3 &4 on the two engines I tested. I have had A/F sensors go bad and cause the horn alarm and after checking the resistance was below 2.0 like 1.0-1.5
I have had good luck replacing OEM A/F sensor with Walker Products Oxygen Sensor - 932-24005 they were made in USA.





 
Really appreciate all that detail. And makes sense on running at 3000 rpm if the motor doesn’t use the sensor until it’s warmed up and at speed. I don’t think I can perform a reset with this tool, I only had a few mins to try it and it’s a little less functional than I hoped (but got a decent deal on it used locally)

Raining here today but I’ll compare with your numbers this week and see what I get. Unfortunately have an open 2” hole in the transom at the moment so can’t drop in the water for a better test.
 
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