[Blue Bowtie]

Welcome Aboard!

Having been on both sides of this situation, I believe it is relevant to remind everyone that intermittent issues are nearly impossible to diagnose unless and until the condition becomes more consistent. While scans and history data stored in the PCM can provide clues, it only indicates what the system has seen and not necessarily its cause.

For example, if an alternator begins to fail and either generates low voltage or applies some AC into the system ground, the PCM will record either low inputs on various sensors, or intermittent/high signals on various sensors. That doesn't mean that all those sensors are failing, since the root cause has absolutely nothing to do with any of them. The same applies to poor connections.

A recent example of that which I had was a Dodge Dakota with numerous and random error codes, accompanied by wandering idle and poor running, barely able to move the vehicle. The FIRST action was to pull the connectors at the PCM and clean corrosion and oxidation. After that, pulling the PCM history and monitoring real-time data made it apparent that a common problem was affecting everything from the TPS and MAP to the O²s and CTS. A little study of the diagrams revealed some potential suspects.

The eventual realization was that the main (upstream) oxygen sensor was randomly getting signals completely out of range. Removing the sensor and bench testing revealed that the 12V sensor heater was bleeding voltage to the sensor element, and that was pulling up the 5V reference supply at the PCM so that all sensors connected to that part of the circuit were getting indiscriminately skewed completely out of range. The owner had already replaced the MAP, two TPS sensors, the CTS, a fuel pressure regulator, and hesitated replacing the MAF and injectors on just a guess because of the high cost of the parts. One new O² solved it all.

In the case of the CTS on GMs, the PCM gets its signal not only from the variable resistor screwed into the water jacket, but through the wiring to and from the sensor, through the connections and splices hidden within the wire harness, through the PCM connectors, relies on the PCM 5V reference supply to be consistent, and requires that components are securely grounded to the chassis AND engine. One poor ground connection at the back of the head and all the sensors could look awry.