P2186: coolant sensor 2 changes faster than its thermal model permits

P2186 is an erratic-circuit code for engine coolant-temperature sensor 2. In the reviewed Diesel L6 ATM–LZO monitor, the controller does not use one fixed temperature-jump limit. It calculates acceptable next-sample bounds from the previous reading and the sensor's time constant.

Dynamic plausibility rather than absolute range

A positive step above the calculated high limit or a negative step below the calculated low limit can qualify. The monitor is intended to recognize a response faster than the sensor should physically produce. A value can therefore remain within an otherwise plausible temperature range while its rate of change is unacceptable.

The configurable channel list assigns the EngCoolantTempSnsr2 function to channel 1. The continuation gives that channel a 5.4-second sensor time constant. That mapping is relevant when selecting scan data: a different temperature channel's smooth behavior does not prove this monitored function is healthy.

Preconditions and useful evidence

Diagnostics must be enabled, and the listed existing erratic and circuit-high/low fault states must not be active. The failure requirement is five seconds within a six-second window, with continuous sampling and Type B reporting over two trips.

Verification should capture the sensor 2 time history and establish that the dynamic check runs without repeated violations. A single steady reading after the event cannot recreate its prior step behavior. The source provides no universal degrees-per-second limit, sensor location or replacement instruction. These facts are limited to the documented LZO configuration; confirm the actual vehicle's function mapping and service procedure before drawing a component-level conclusion.

Source: GM monitor, PDF page 793; GM continuation, PDF page 794.