Date: 201810
Local time of day: 1201-1800
Location: ZZZ.TRACON, US
Flight conditions: IMC
Weather elements / visibility: 10
Light: Daylight
Aircraft: Skyhawk 172/Cutlass 172
Operator: Personal
Operating under: Part 91
Flight plan: IFR
Mission: Training
Flight phase: Cruise
Airspace: Class E ZZZ
ATC / advisory: TRACON ZZZ
Reporter organization: Personal
Reporter function: Pilot Flying; Single Pilot
Reporter qualification: Flight Crew Instrument; Flight Crew Private
Human factors: Troubleshooting; Human-Machine Interface
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter VFR In IMC
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Landed As Precaution; Flight Crew Took Evasive Action
Contributing factors: Equipment / Tooling
Primary problem: Equipment / Tooling

Narrative: During flight in IMC conditions on a segment of the IFR flight to ZZZ; the Mode 'C' transponder began to display different types of altitude that was different from the altimeter. Approach contacted me about the issue and I reset the transponder during the flight but that did not resolve the issue about the changing altitudes. When I pressed the PTT [Push To Talk] to advise Approach; the G430 screen reset itself during the flight. In this particular aircraft; the G430 screen has the only communication radio and navigation radio in addition to the GPS equipment that I was using for the flight. After the GPS unit reset itself; I called Approach and told them the Mode C transponder was turned off and back on but the issue was not resolved.Once again; I pushed the PTT button to transmit; the GPS screen turned off and remained off. Once this occurred; I made the decision to get out of IMC conditions so I descended to 3;500 feet into VFR conditions. At this point of the flight; I just passed ZZZ airport and I made a mental note of where the nearest airport was at. Approach asked me where I was at in altitude and I told them I was 3;500 feet due to the GPS screen was not functioning properly and I was not going to be in IMC conditions with this issue. I made up my mind that I did not want to continue the flight and I asked for a priority landing at ZZZ so that I can attempt to determine the problem or call the mechanic and explain the situation. Approach either didn't hear my request or was too busy with other things; so I am not sure if my request was heard. I was able to communicate with Approach with a black screen on the GPS unit during this time.About 2-3 minutes later; the communication was lost with Approach and I was not able to hear them or talk. I told Approach I am canceling the IFR flight plan and diverting to ZZZ for a landing. Another aircraft on the same frequency that I was on relayed from ZZZ Tower that I was cleared to land on any runway. I relayed that I acknowledge the message and told the plane that I have limited to no communications and no GPS screen which has the communication and navigation radio channels. The other aircraft told me I was cleared to land on any runway; so I made a landing on RWY XX where I was met by the fire department and an Operations personnel. I told them no one was injured; nor the aircraft; nor was there any fire or damage to the aircraft; just a communication and GPS screen issue.I was escorted to the FBO by the Operations personnel where I made a phone call to the flight school and expressed the issues I had during the flight. I honestly don't know what caused the issue nor do I know what could have been done to prevent the issue from occurring in the future.




Synopsis: C172 pilot reported having transponder issues; then additional equipment problems having to land to determine what was wrong with the aircraft.