Ihave a 2006 496 and after getting steady beeps hooked it to diacom. We checked the cooling system and everything seems fine. No clogs,brand new impeller and thermostat.
I got these codes from diacom. Please help.

shift switch
prt emct overheat
overspeed
stb emct overheat

The overspeed is most likely from revving the motor too high in neutral and you can clear this code. Prt emct and Stbd emct overheat are port and starboard exhaust mainfold coolant temperature overheat. This is a common problem on the bravo setup when both port and stbd overheat at the same time. The most likely cause of this is the 3/4 inch water inlet hose where it meets the transom assembly. There is a tapered insert inside of that hose that seals it to the trans assy. If used in salt water there is a tendancy for salt corrosion to build between the hose and the trans assy. This in turn crushes the tapered insert leaving a hose diameter of about 3/8 of an inch at the transom. Motor will run fine on the hose and at idle but after high speed runs you'll get an alarm. All of the flushing in the world will not stop this as the salt is only being removed from the inside of the water hose and passages. It is a good idea to thouroughly hose off the drive and inside of the outer part of the transom assembly after running the boat. If you're a DIY guy, get over the back of the motor and remove the water elbow. You;ll need to unclip the red 1 1/4 inch hose first. Once you remove the elbow you should be able to feel the tapered insert. You won't be able to see in the hose because of the angle but you should be able to get your forefinger in to at least the first joint. If you see corrosion around the outside of the hose and the hole feels smaller than about 5/8 inch youl need to pull the drive, remove the hose, clean up around the trans assy where the hose fits in, replace the hose and tapered inserts. Not sure on the shift switch. Is this a DTS shift and throttle package?

You didn't have the engine down recently for anything did you? Also do you have a sea strainer? Just wondering if you sucked up any dirt, debris, etc.? Did you pull the water lines that go to you exhaust and make sure you have sufficient water flow? Also you could install a water pressure gauge inexpensively even if it's not the problem now it's always nice for a little extra insurance. Is it possible it could be a bad sender?

I see your relatively new to the board however Raylar might be a good person to ask. Just PM him.

Good luck and keep us posted.

John

I was posting during the same time however this post is good.

Are you running this on the hose or are you in the water? Is there water coming out the exhaust?

On 496's I have also seen a lot of boaters put a new impellor in the raw water pump even though the end plates on the pump were deeply grooved and scared. In this condtion the pump will not pump enough water at sufficient pressure to feed the cooling system and the engine will overheat at the exhaust manifolds very quickly and throw this exhaust manifold coolant temperature alarm code.
Make sure you use a scanner and check the water pressure value and make sure its in conformance to Mercury's minimum pressures. The shift switch code should mean your Bravo shift plate (neutral lockout) switch is either disconnected or not working properly. Don't forget to clear the codes once you've checked all items and made neccessary repairs or corrections. then re-run the engine and recheck for open codes.

Best Regards,
Ray @ Raylar

Best Regards,
Ray @ Raylar

Thank you for the replies. I am trying to post the diacom readings so you can see all parameters. I will post that later. The sea pump pressure reads between 3 and 5 psi. This seems low? I bought this boat last year and changed the impeller. There were no signs of wear whatsoever. The whole pump looked brand new in and out. There are no signs that it was ever operated in salt and found maps of lakes in the boat so i think it was operated in lakes. Is there possibly something stuck in the transom intake? This happens when i run the boat at full trotthle above 4000 rpm. Up to 4000 rpm the temp guage reads about 180. I have not run the boat with diacom but only scanned it in my garage. See the diacom report.

DIACOM MARINE SERVICE REPORT

02/19/2010 12:26:01


1. VEHICLE CONFIGURATION

Cust. Name:
Engine Make:
Engine Serial No:
Model Year:
System Type: MerCruiser PCM555

2. PERFORMANCE DATA

Parameter Description Value Unit

Engine Speed 0 RPM
Available Power 100 %
Coolant Temperature 86.00 °F
Fuel Flow Rate 0.00 GPH
Port Exhst Cool Temp 84.20 °F
Sea Pump Pressure 0.00 PSI
Starb Exhst Cool Temp 84.20 °F
IAC Duty Cycle 0.00 %
Manifold Absolute Pressure 14.50 PSI
Trim Position 706 #
Baro Pressure 14.55 PSI
Trim Volts 3.52 VDC
Manifold Air Temperature 87.80 °F
Pitot ADC 0 #
Oil Pressure 0.66 PSI
Paddle Wheel 0 Hz
Throttle Position 0.00 %
Sensor Power 5.00 VDC
Throttle Sensor Voltage 0.56 VDC
Lake/Sea Temp 431.60 °F
Spark Advance 6.00 DEG
Fuel Level 1022 #
Battery Voltage 12.52 VDC

3. TROUBLE CODE STATUS

Current ECM Codes

Sensor Fault, click Read Fault button for details

Freeze Frame Data:

0 FUEL LVL2 CKT H
--------------------------------------------------------------------
FF Baro Pressure 14.55 PSI
FF Battery Volts 12.27 VDC
FF Sea Pump Pressure 0.00 PSI
FF Boat Speed 0.00 #
FF Manifold Air Temp 84.20 °F
FF Coolant Temp 84.20 °F
FF Demand 0.00 %
FF Engine Speed 0 RPM
FF Engine State Stall
FF FPC Total 0.0 Counts
FF Frequency Count 552
FF Fuel Level 0.00 %
FF Gear Position Neutral
FF Lake Temp 429.80 °F
FF Engine Load 0.00 %
FF Main Pwr Relay Requests 32772.0
FF Manifold Air Pressure 14.56 PSI
FF Oil Level 0.00 %
FF Port Tab Pos 0.00 %
FF Available Power 100 %
FF Run Time 98.97 hrs
FF Starboard Tab Pos 0.00 %
FF TPS Percent 0.00 %
FF Trim Position 84.67 %

1 STEER CKT HI
--------------------------------------------------------------------
FF Baro Pressure 14.55 PSI
FF Battery Volts 12.27 VDC
FF Sea Pump Pressure 0.00 PSI
FF Boat Speed 0.00 #
FF Manifold Air Temp 84.20 °F
FF Coolant Temp 84.20 °F
FF Demand 0.00 %
FF Engine Speed 0 RPM
FF Engine State Stall
FF FPC Total 0.0 Counts
FF Frequency Count 461
FF Fuel Level 0.00 %
FF Gear Position Neutral
FF Lake Temp 429.80 °F
FF Engine Load 0.00 %
FF Main Pwr Relay Requests 32772.0
FF Manifold Air Pressure 14.56 PSI
FF Oil Level 0.00 %
FF Port Tab Pos 0.00 %
FF Available Power 100 %
FF Run Time 98.97 hrs
FF Starboard Tab Pos 0.00 %
FF TPS Percent 0.00 %
FF Trim Position 84.67 %

2 FUEL LVL CKT HI
--------------------------------------------------------------------
FF Baro Pressure 14.55 PSI
FF Battery Volts 12.22 VDC
FF Sea Pump Pressure 0.00 PSI
FF Boat Speed 0.00 #
FF Manifold Air Temp 84.20 °F
FF Coolant Temp 84.20 °F
FF Demand 0.00 %
FF Engine Speed 0 RPM
FF Engine State Stall
FF FPC Total 0.0 Counts
FF Frequency Count 510
FF Fuel Level 0.00 %
FF Gear Position Neutral
FF Lake Temp 429.80 °F
FF Engine Load 0.00 %
FF Main Pwr Relay Requests 32772.0
FF Manifold Air Pressure 14.54 PSI
FF Oil Level 0.00 %
FF Port Tab Pos 0.00 %
FF Available Power 100 %
FF Run Time 98.97 hrs
FF Starboard Tab Pos 0.00 %
FF TPS Percent 0.00 %
FF Trim Position 84.83 %

3 PITOT CKT LO
--------------------------------------------------------------------
FF Baro Pressure 14.55 PSI
FF Battery Volts 12.25 VDC
FF Sea Pump Pressure 0.00 PSI
FF Boat Speed 0.00 #
FF Manifold Air Temp 84.20 °F
FF Coolant Temp 84.20 °F
FF Demand 0.00 %
FF Engine Speed 0 RPM
FF Engine State Stall
FF FPC Total 0.0 Counts
FF Frequency Count 511
FF Fuel Level 0.00 %
FF Gear Position Neutral
FF Lake Temp 429.80 °F
FF Engine Load 0.00 %
FF Main Pwr Relay Requests 32772.0
FF Manifold Air Pressure 14.55 PSI
FF Oil Level 0.00 %
FF Port Tab Pos 0.00 %
FF Available Power 100 %
FF Run Time 98.97 hrs
FF Starboard Tab Pos 0.00 %
FF TPS Percent 0.00 %
FF Trim Position 84.83 %

4 GUARDIAN
--------------------------------------------------------------------
FF Baro Pressure 14.53 PSI
FF Battery Volts 14.00 VDC
FF Sea Pump Pressure 3.88 PSI
FF Boat Speed 10.00 #
FF Manifold Air Temp 138.20 °F
FF Coolant Temp 167.00 °F
FF Demand 87.08 %
FF Engine Speed 3978 RPM
FF Engine State Running
FF FPC Total 75.7 Counts
FF Frequency Count 6
FF Fuel Level 0.00 %
FF Gear Position In Gear
FF Lake Temp 431.60 °F
FF Engine Load 40.75 %
FF Main Pwr Relay Requests 33812.0
FF Manifold Air Pressure 13.83 PSI
FF Oil Level 0.00 %
FF Port Tab Pos 0.00 %
FF Available Power 47 %
FF Run Time 97.10 hrs
FF Starboard Tab Pos 0.00 %
FF TPS Percent 87.08 %
FF Trim Position 0.00 %

FF Battery Volts 12.68 VDC
FF Sea Pump Pressure 1.91 PSI
FF Boat Speed 0.00 #
FF Manifold Air Temp 141.80 °F
FF Coolant Temp 168.80 °F
FF Demand 11.51 %
FF Engine Speed 3056 RPM
FF Engine State Running
FF FPC Total 39.7 Counts
FF Frequency Count 56
FF Fuel Level 0.00 %
FF Gear Position Neutral
FF Lake Temp 431.60 °F
FF Engine Load 21.50 %
FF Main Pwr Relay Requests 33812.0
FF Manifold Air Pressure 8.32 PSI
FF Oil Level 0.00 %
FF Port Tab Pos 0.00 %
FF Available Power 100 %
FF Run Time 89.45 hrs
FF Starboard Tab Pos 0.00 %
FF TPS Percent 11.51 %
FF Trim Position 84.67 %

6 STB EMCT OVRHT
--------------------------------------------------------------------
FF Baro Pressure 14.53 PSI
FF Battery Volts 14.11 VDC
FF Sea Pump Pressure 1.70 PSI
FF Boat Speed 0.00 #
FF Manifold Air Temp 129.20 °F
FF Coolant Temp 186.80 °F
FF Demand 8.10 %
FF Engine Speed 689 RPM
FF Engine State Running
FF FPC Total 38.2 Counts
FF Frequency Count 2
FF Fuel Level 0.00 %
FF Gear Position In Gear
FF Lake Temp 429.80 °F
FF Engine Load 18.20 %
FF Main Pwr Relay Requests 33812.0
FF Manifold Air Pressure 9.86 PSI
FF Oil Level 0.00 %
FF Port Tab Pos 0.00 %
FF Available Power 5 %
FF Run Time 92.15 hrs
FF Starboard Tab Pos 0.00 %
FF TPS Percent 8.10 %
FF Trim Position 12.90 %

7 OVERSPEED
--------------------------------------------------------------------
FF Baro Pressure 14.53 PSI
FF Battery Volts 14.16 VDC
FF Sea Pump Pressure 3.80 PSI
FF Boat Speed 7.00 #
FF Manifold Air Temp 136.40 °F
FF Coolant Temp 167.00 °F
FF Demand 18.86 %
FF Engine Speed 1271 RPM
FF Engine State Running
FF FPC Total 54.2 Counts
FF Frequency Count 151
FF Fuel Level 0.00 %
FF Gear Position In Gear
FF Lake Temp 431.60 °F
FF Engine Load 28.61 %
FF Main Pwr Relay Requests 33812.0
FF Manifold Air Pressure 12.16 PSI
FF Oil Level 0.00 %
FF Port Tab Pos 0.00 %
FF Available Power 100 %
FF Run Time 97.12 hrs
FF Starboard Tab Pos 0.00 %
FF TPS Percent 18.86 %
FF Trim Position 3.38 %

8 PRT EMCT OVRHT
--------------------------------------------------------------------
FF Baro Pressure 14.50 PSI
FF Battery Volts 12.41 VDC
FF Sea Pump Pressure 0.00 PSI
FF Boat Speed 0.00 #
FF Manifold Air Temp 122.00 °F
FF Coolant Temp 195.80 °F
FF Demand 0.12 %
FF Engine Speed 0 RPM
FF Engine State Stall
FF FPC Total 0.0 Counts
FF Frequency Count 19
FF Fuel Level 0.00 %
FF Gear Position Neutral
FF Lake Temp 431.60 °F
FF Engine Load 0.00 %
FF Main Pwr Relay Requests 32772.0
FF Manifold Air Pressure 14.50 PSI
FF Oil Level 0.00 %
FF Port Tab Pos 0.00 %
FF Available Power 5 %
FF Run Time 95.07 hrs
FF Starboard Tab Pos 0.00 %
FF TPS Percent 0.12 %
FF Trim Position 19.35 %

9 SHIFT SWITCH
--------------------------------------------------------------------
FF Baro Pressure 14.53 PSI
FF Battery Volts 13.92 VDC
FF Sea Pump Pressure 5.17 PSI
FF Boat Speed 0.00 #
FF Manifold Air Temp 87.80 °F
FF Coolant Temp 87.80 °F
FF Demand 28.10 %
FF Engine Speed 3583 RPM
FF Engine State Running
FF FPC Total 43.5 Counts
FF Frequency Count 0
FF Fuel Level 0.00 %
FF Gear Position Neutral
FF Lake Temp 431.60 °F
FF Engine Load 20.38 %
FF Main Pwr Relay Requests 33812.0
FF Manifold Air Pressure 7.87 PSI
FF Oil Level 0.00 %
FF Port Tab Pos 0.00 %
FF Available Power 100 %
FF Run Time 88.17 hrs
FF Starboard Tab Pos 0.00 %
FF TPS Percent 28.10 %
FF Trim Position 84.19 %

Fault Log Data
Fault Descriptions Seconds

Battery Range High: 0
Battery Range Low: 0
Block Pressure is Low: 0
Compressor Temp Overheat: 0
ETC Motor Open: 0
ETC Motor Short: 0
Fuel Pressure Sensor Input High: 0
Fuel Pressure Sensor Input Low: 0
Guardian Strategy: 116
Knock Sensor 1: 0
Knock Sensor 2: 0
Low Oil Pressure Strategy: 0
Low Oil Remote Strategy: 0
Low Oil Reserve Strategy: 0
MAP Sensor 1 Input High: 4
MAP Sensor 1 Input Low: 0
MAP Sensor 1 Idle Rational: 0
Oil Pump Output: 0
Overspeed: 74
Port Clnt Overheat: 0
Starboard Clnt Overheat: 79
Warning Horn Output: 0
Water In Fuel: 0

Engine Run Time History:

Total engine run time: 98.97 Hours
0 - 749 RPM: 34.80 Hours
750 - 1499 RPM: 12.40 Hours
1500 - 2999 RPM: 22.40 Hours
3000 - 3499 RPM: 13.48 Hours
3500 - 3999 RPM: 8.23 Hours
4000 - 4499 RPM: 5.42 Hours
4500 - 4999 RPM: 2.23 Hours
5000 - 5499 RPM: 0.00 Hours
Over 5499 RPM: 0.00 Hours

I had a similar problem to this myself on my 496HO, turned out to be a partial blockage of the heat exchanger which is like a honeycomb inside, with passages only about 5 or 6mm in diameter. Rectified it by taking the end caps off of the exchanger, and using an air compressor to blow out all of the passages. Hope this helps, had me stumped for quite a while. Regards Jeremy.