C12 engine code 25

[steve zannella]

We're stuck in Vegas with a check engine code 25.  The coach runs fine except when I attempt to engage cruise control the check engine light flashes 25. We drove with the error code for about 2 hours with no loss of performance. The Cat manual says boost pressure sensor low power. I checked engine monitor was getting 28 psi boost going up a 6 percent grade at 55 mph, max power at 99 percent.

Is this something we limp home with or fix it now situation.

All comments appreciated

[Gerald Farris]

Steve,
I had a similar problem on my 2000 model C 12 and it turned out to be nothing wrong with the engine, but the Smart Wheel module was malfunctioning. A few questions, does the engine ECM have a stored DTC (diagnostic trouble code)? If so a Cat dealer can tell you the conditions that the code was set under, and the frequency of the malfunction. Also, does the check engine light only come on when you try to engage the cruse control?

I can not advise you to continue driving a coach with the check engine light on, but if the light only comes on when you engage the cruse control, I would have no issues with driving it home, or at least to a Cat dealer that I preferred.

Gerald

[steve zannella]

Thanks Gerald the error code only flashes when cruise is trying to set otherwise no check engine light.

[steve zannella]

Gerald
An update went to cat repair shop and ecu only had 1 fault. they checked the turbo for leaks and found none. so i think it must be the smart wheel controller.

thanks for the help

steve

[Edward Buker]

Steve, Gerald,

This is likely a good example of information going down a buss or electrical noise attaching to a buss that creates an error code. When you think about the turbo boost pressure, the reality is to expect a relatively slowly changing pressure related to the amount of exhaust gas pressure that is driving the turbo. The moment that you press the cruise control on the Smart Wheel, to turn it on, can have no affect on the real boost pressure so there can be no other interpretation other than a system error was made in creating this code. The Smart Wheel may have a relay with a little contact arc or a relay contact with some bounce in it that created some electrical noise on the Cat ECU data buss.

Gerald I would be curious as to what solved your problem or if it just went away....

Later Ed

[Gerald Farris]

Ed,
My problem started with the check engine light when the cruse control was engaged, and quickly evolved into several issues over a few thousand miles, like the horn blowing when the cruse control was engaged or when the wipers were turned on. The correction was replacing the Smart Wheel module.

Gerald

[steve zannella]

Ed, Gerald

since we left Vegas with no definitive knowledge as to what happened except that the error code was not an ongoing problem, we have moved on to cooler climate 90 vs 112 degrees, the cruise control works fine for now also the kenwood monitoir was not working properly and now works.

Electrical gremlins temperature sensitive?

Steve

[Edward Buker]

Steve,

There is a temperature spec that semiconductor parts get tested to or a simulation is done and a guard band is derived that assures an operating spec range. At 112 outside I am not sure what the electrical bay compartment is running with no ventilation while on the road and maybe sun on it. I think your smartwheel unit may be in there. Any item with electronics within that compartment is creating heat and at the semiconductor device level enclosed within an electrical unit it can even be substantially hotter. I have seen electronics get wonky from heat, not operate properly, and recover when cooled down. It usually is caused by operating temperatures beyond the spec that was assured at the time of testing so that the part is no longer within the test spec at that temperature. All these circuits are timed to work together and turn on and off at certain voltage levels and all of that gets shifted by temperature so it is possible that heat made the Gremlin and cooler operating temps have parts operating back in spec. If things get too hot you can induce a permanent fail but that is another story....hopefully you are good to go.

Later Ed