With the engine coolant heater plugged in, the coolant will read that.
Below is some information on that code.
This is a crank no start?
PIT4090: SES MIL DTC U0100 U0101 U0105 and/or U0106 - keywords communication erratic low power shift - (Jul 27, 2006)
|Subject:||SES MIL DTC U0100 U0101 U0105 and/or U0106|
|Models:||2004-2005 Chevrolet Silverado |
The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.
Some owners may comment of a SES MIL on and if DTCs are checked with the Tech 2 a U0100, U0101, U0105, and/or U0106 will be set. The ECM, TCM, FICM, and Glow Plug Controller communicate between each other on circuits 2361 and 2362 (CAN Buss), the Tech 2 does not communicate on these circuits.
In most cases, if all the DTCs set it could be caused by the Can Buss circuits shorted to ground. Cases for either of these circuits shorting to ground at the FICM/Alternator bracket have been reported. Before replacing any parts perform a thorough visual inspection of this wiring harness near the FICM/Alternator bracket and repair as necessary if shorted.
Glow Plug System Description
In the diesel engine, air alone is compressed in the cylinder. Then, after the air has been compressed, a charge of fuel is sprayed into the cylinder and ignition occurs, due to the heat of compression. Eight glow plugs are used as an aid to starting.
Control of the instant start system (ISS) glow plugs is accomplished by a glow control module unit and 4.7 volt glow plugs, requiring 2 seconds to heat up to 1,000°C (1,832°F). The temperature and the power consumption is controlled between the engine control module (ECM) and the controller within a wide range to suit the engine's pre-heating requirements. Each glow plug is energized individually. This capability yields more optimum heat times for the glow plugs, thus pre-glow times can be kept to a minimum for short wait to crank times and maximum glow plug durability. A DTC will set if there is a glow plug system fault.
A normal functioning system operates as follows:
| • ||Turn the ignition ON with the engine OFF, and at room temperature.|
| • ||The glow plugs turn ON and heat up in 2 seconds and then are pulse-width modulated (PWM) for another 2 seconds.|
| • ||The glow plug wait lamp is ON for 1 second during cold start.|
| • ||The glow plug wait lamp may not illuminate during a warm engine start.|
| • ||If the engine is cranked during or after the above sequence, the glow plugs may cycle ON and OFF after the ignition switch is returned from the start position, whether the engine starts or not. The engine does not have to be running to terminate the glow plug cycling.|
The glow plug initial ON time will vary based on the system voltage and temperature. Lower temperatures cause longer ON times.
The ECM provides glow plug operation after starting a cold engine. This post-start operation is initiated when the ignition switch is returned to Run, from the Start position. This function helps clean up excessive white smoke and/or poor idle quality after starting.
The glow plugs are 4.7 volt heaters in each of the cylinders that turn ON, then pulse-width modulated when the ignition switch is turned to the RUN position prior to starting the engine. They remain pulsing a short time after starting, then they are turned OFF.
A Wait to Start lamp on the instrument panel provides information on engine starting conditions. The Wait to Start lamp will not illuminate during post-start glow plug operation.
The glow plug controller is a solid state device which operates the glow plugs. The glow plug controller is connected to the following circuits:
| • ||The fuel heater ignition 1 voltage circuit|
| • ||The battery voltage circuit|
| • ||The CAN communication circuit located between the engine control module (ECM) and the glow plug controller|
| • ||The engine ground circuit|
| • ||The glow plug supply voltage circuits located between the glow plug controller and the glow plugs.|
The glow plug diagnostic circuits are directly monitored individually by using a separate transistor to control current to each glow plug. Individual diagnosis is thus possible for every glow plug.