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The following tests are used to inspect the probes and harness leads. In most cases, the cause of missing EGT, TIT, or CHT readings can be attributed to a problem involving the probes or harness wiring.

• Disconnect probe from harness wiring. Measure the resistance of the probe between the two leads. Correct reading should be less than a couple of ohms.
• Measure the probe for correct grounding. Measure the resistance from one of the probe leads to the engine case. This reading should be less than 10 ohms.
• If measurements above are good, remove the probe. Connect a meter across the two probe leads. Heat the probe using a torch or lighter. The resistance should always be less than a couple of ohms.
• Inspect the wiring harness for breaks and good crimps. Pull tautly on the crimp. It should not separate from the wire. Ensure that the wire is not pinched or broken. The wiring harness should not be bundled with ignition leads, P-leads, alternator wiring, or battery wiring.
• Inspect the pin connections at the instrument connector. Ensure that the pins make good contact with the circuit board. Tug on the wire. It should not pull free from the connector or pin.
• Harness leads can be difficult to troubleshoot. In most cases, it is ideal to replace the possible problematic wire with a new one. Please note that probe wiring cannot be spliced.
• Inspecting OAT Probe - OAT Test

• OAT Probe

  How does the OAT probe operate

  The Insight 1200-021 OAT probe is not a resistance type. It is a semi-conductor, output current proportional to absolute temperature type. The probe has a sensitivity of one micro-amp (1 uA) per Kelvin, and requires a minimum of four Volts (4V) to operate. For example at 0 Celsius (273 K) the probe draws 273 micro-Amps.