EGT / CHT probes are thermocouple devices and typically  The EPI800 and VM1000 systems check for an open probe when the system is first turned on. A probe that does not pass the checks is displayed as ‘Er’ in the corresponding cylinder switch position(s) on the EPI800 system and as a blank bargraph(s) on the VM1000 system.

If a probe becomes intermittent or fails inflight, the reading may appear as a random fluctuation in temperature which can climb very high or dip very low. If this occurs, you can re-cycle power and the system will attempt to recheck the probes. If the problem is constant, you have the best chance of identifying the errant probe(s), otherwise it may take some trial and error troubleshooting. The following steps will help you troubleshoot the suspected probe(s):

1. With the engine off, turn power ON to the engine instruments. After a short period of time, the system will be running.

2. Scan all CHT and EGT positions for ‘Er’ (EPI800) or blank graph (VM1000).  If all positions are ‘Er’ there is most likely  a DPU fault and the troubleshooting process can be stopped and the factory contacted. If not, the probe circuit(s) may be open. Perform the following test sequence for each suspected probe:

(a.) Shut off power.
(b.) With digital meter, measure resistance between suspect probe(s) leads, while still connected, at proper DPU terminals. Resistance should be less than 10 ohms.________
(c.) If yes, then record the resistance and contact the factory.__________
(d.) If not, then CHECK ALL CONNECTION POINTS for a clean secure connection. Because of the type of metals used in thermocouples, the leads can corrode and/or rust and must be scraped clean. Accomplish this and re-try from #1.

(e.) If the above step does not result in a solution, then the probe can be considered bad and no further troubleshooting is needed. Replace the probe.

(f.)  Measure for resistance to aircraft ground bus from each probe lead. This resistance check should be made on the 2 meg ohm scale of the meter. This value should be greater than 1 meg ohm. If not then the probe should be replaced.