Sean Miller IAT 1, IAT 2 (if used) and ECT at 35 deg. F., OAT / AAT data supplied to the ECM / PCM from the IPC / BCM / HVAC is reading 50 deg. F. The PCM knows that can't be right. That value is then put into failsoft mode and substituted with a more believable value. The raw data value should be in the PCM's global / generic OBD II PID list if the OEM put that PID there to begin with. Now any tech that looks at a bunch of temperature readings in one or more modules after a vehicle has been shut down overnight should be able to spot the one that is WAY off but not ridiculously off. That's the work around. 4. Usually a skewed sensor is just a bad sensor. When diagnosing sensor problems, always make sure there is not excessive resistance in a connection or the wiring itself. (Figs. 6-9) While not applicable to OAT / AAT sensors, sensors that measure the temperature or pressure of a liquid (engine coolant, high pressure motor oil, etc.) can leak. Sometimes that leak ends up wicking its way through the wiring. While this wicking can be only a few inches of wiring, sometimes that liquid can wick its way into the module. Other times sensor wiring and connections (including the OAT / AAT) can be contaminated by a leak from something else such as battery acid or windshield washer fluid and the same demise can occur. While you might expect the connection at that sensor to be obviously contaminated / corroded, this is not always the case. While rare, this type of resistance inducing wiring contamination can usually be found if the pair of wires going Sean Miller Figure 7: . Solder and heat shrink tubing is a superior alternative. Sealed butt splicers are a better choice but care must be taken in order for the splice to truly seal . The splicer seal in this photo did not get shrunk / sealed properly and is full of resistive corrosion. Sean Miller Sean Miller Figure 8: Visually inspecting terminals inside connectors. Figure 6: Master technician Sean Miller shared these photos of corrosion that caused voltage drops and vehicle problems. Circuits exposed to undercar / underhood environments should not be repaired with crimp / butt splice connectors. Figure 9: This connector should be replaced along with a portion of the wiring harness to prevent future problems. March 2017 5 MACS Service Reports