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Check a plug-in probe connection

Connect the correct probe before switching on.

testo 435 family

Applies to: 435-1 / -2 / -3 / -4, using compatible plug-in probes.

Before you start: Switch off before connecting. Check compatibility for your exact variant. Keep the rear magnets at least 15 cm from pacemakers.

Find the probe sockets

The plug-in sockets are at the base, marked 5 in the overview.

testo 435 overview with callout 5 below the instrument marking the probe sockets at its base.
Base connections: callout 5. Testo manual, page 6 ↗ · Select image to enlarge.

Connect before power-on

Connect the appropriate plug-in probe, then switch on so the instrument can recognize it.

Check the display

Record the detected probe or error. Radio probes use a separate module and setup in the manual.

If the issue continues: If the probe is not recognized, request assessment with the 435 variant, probe part number and exact message.

Still need help with your device?

Include the model, serial number, exact error and checks already completed.

Start a service request

Source and applicability

testo 435 - Multifunction measuring instrument: Instruction manual — §3.1, p. 6; §3.2, p. 8; §5.1, p. 10. 0977 4350 en 08 V02.10 en

Open the complete Testo operating manual ↗ · Find this model in the manual list

QRM wording summarizes the checks. Diagram excerpts © Testo SE & Co. KGaA. Follow the complete manual and warnings for your instrument. Source checked 7 September 2026.