MAP Sensor 1 Input High: 25


Is this a problem? It looks like everything else reads 0 seconds?

MAP Input Hi with a frequency count of 46 and last occurance about 1.4 engine hours ago. I think that (MAP sensor) is your issue right there.

Service Manual says:
Loose connection, corrosion, open (Lo) or Short (Hi) in circuit. Inspect circuit, Repair or replace harness.

Faulty Sensor. Replace sensor.

Dave

Thanks Dave! Do you know where the MAP sensor is?

It is under the cover towards the back of the intake manifold.

Dave

I had the same exact problem. I still have not figured out what was the problem, I thought it was bad gas. So I added 91 in it and took it back out. It ran fine no beeps? I still want to have it scanned to see why it did that but I know its a faulty sensor.

Thats a hellof alot of info there


Rob

Hey Dave,

I made sure the map sensor was plugged in securely and I have not had a problem in over 4 hours of run time. I got the manual you suggested and it says that pressure reading should be between 8.41-8.99 at idle. I'm seeing slightly higher (9's) according to Diacom. As soon as I come slightly off idle it drops down into the 8's. I'm going to assume that everything is OK right now.

One more question. There is a "transom harness" that T's off to two connectors that are not plugged into anything. I guess that is what is giving me the "Trim Ckt Lo" and the "Steer Ckt Hi" codes. Can I just unplug and remove that harness so I don't have those connections bundled up in my engine compartment? Is there a way to put those connectors in "loop back" or something so those codes don't appear?

Why does Diacom say Lake/Sea temp 431*?


Thanks,
Dave M.

Dave,

Good to hear you have made progress. Your MAP readings are consistant with the 496HO's that I have seen. They all seem to be around 9 to 9.5 PSI at idle (sea level).

You could disconnect the transom harness, but your may be using the mechanical throttle and shift trim limit connections (purple and blue wires with bullet connectors that connect to the trim pump). Check page 3A-32 in the diagnostic manual.

I have talked to an engineer at Merc and he said that there is no way to prevent fault codes (such as Trim Ckt Lo and Steer Ckt Hi) due to missing sensors. In the case of the Sea Temp reading, without a sensor connected the ECM does not trigger a fault code, it just shows a default value of 431 degrees.

Dave

Thanks Dave! I don't have a trim limit, or "trailer" button. I have mechanical indicators so I cut the trim sender and limit wires out.

I'll try disconnecting that harness and see if anything happens. I just don't want it dangling back there if I don't need it.

Gotta love this technology. It takes the guess work out of things. I highly recommend the Diacom SW.

Dave M.