After replacing injector lines a couple weeks ago (late at night) I shut the hood and took the truck for a spin. The truck ran fantastic, as it always has. The ses light was on but I assumed it was because of my glow plug heater circuit A, which I haven't had the chance to fix yet. After checking codes, there was a code for the MAF and the MAP. I forgot to plug both of them back in! Doing some research on lb7s in general, this should either make them smoke like a train or run very poorly. Neither one occured. The truck had no power loss or noticeable increase in smoke. Bottom line is, why would two important sensors not working not cause any issues at all?

 

Alot of times when a cold engine is fired up they have what is called a default run cycle which only read a few sensors until up to a certain temp. Then it will start kicking on the other sensors and more finely tune itself. Not sure if these trucks are that way or not as I've been a dodge and ford diesel guy for quite a while and just bought my first d max as my chevy love will never die. I'm starting my extensive interweb reads learning the d max stuff.

 

that is basically correct.

for the LB7 duramax, the MAF sensor tests require that the coolant and air temp be above -4 degrees. then if it is out of range for more then 100 tests it will set a CEL. i have no clue as to how often it does the MAF check but i seen it go off in less then 5 minutes of unplugging the MAF

for the MAP, ECT must be above 140, RPM between 500 and 3600, engine must be running for at least 1 second. then the test is over 5.1 or under 5.1 PSI as compared to the desired boost amount before CEL is set

 

Hi I know this is an old post but I'm having similar problems. My truck is stuck in that default run cycle. 850 rpm idle...loud as if its cold, shift issues, and the GP cycles every start, regardless. Scan showed a code for thermostats? but showed coolant temp at -50 C so I changed the temp sensor. Still the same.Can u point me to some info on how that default mode works? I'm thinking this is all relevant to my issue. Any help appreciated. Thanks Cory

 

Double check the terminals at the sensor. Make sure they're not spread open in the connector. Also make sure the wires aren't broke inside the insulation at the, especially at the sensor end. you may also need a scan tool to check the reading or a meter to check the voltage to the sensor