Bosch Microwave E4: The Thermistor Circuit Reads Shorted

What E4 means

This code appears on Bosch built-in speed microwave ovens when the thermistor circuit looks shorted, the mirror image of the open-circuit version. The display shows E4 for three seconds and the oven reverts to plug-in mode. A shorted sensor reports an absurdly high temperature, so the control disables convection and combination functions instead of letting them run on a bad reading. Basic microwaving continues.

Common causes of E4

Thermistor shorted inside
Sensor wire pinched against the metal cavity
Input module reading the circuit incorrectly

✓ One safe check you can try

1. Turn the oven off at the breaker for two minutes, then back on; try this once. 2. Run a plain microwave cycle to see that the basic function works. 3. Leave the housing closed. The high-voltage capacitor stays charged after disconnection, and discharging it is a job for a technician. 4. If E4 returns, call us.

! Why to stop there

Discharging the capacitor safely requires tools and training, so opening the oven is risky.
A pinched wire and a shorted sensor give the same reading without a meter.
Wrong guesses can mean replacing a control module that was never the problem.

Opening a panel yourself does not automatically cancel a manufacturer warranty, but it can cause accidental damage, and some manufacturers set their own service conditions. Check your warranty terms, or ask us, before deciding.

→Same appliance

Other Microwave codes

E1Bosch Microwave E1: Thermistor Circuit Reads Open E-04Bosch Microwave E-04: Over-the-Range Humidity Sensor Not Reporting E-11Bosch Microwave E-11: Over-the-Range Key Read as Held for a Minute E2Bosch Microwave E2: The Safety Shutoff Stopped Your Cycle E3Bosch Microwave E3: Door Will Not Latch or Release Properly E11Bosch Microwave E11: Moisture Detected at the Control Panel E17Bosch Microwave E17: The Fast Preheat Did Not Finish ER1Bosch Microwave ER1: Convection Temperature Sensor Failing

E4E4 questions

What is the difference between E4 and E1?

E4 means the sensor circuit reads shorted, while E1 means it reads open. Both disable convection and combination modes, but the repair differs, so a technician measures which applies.

Can I keep microwaving with E4?

Usually plain microwave cooking still works, since the code concerns the temperature sensor. If the oven behaves oddly in any mode, stop and call us.

Is it worth repairing this built-in oven?

Often, since a sensor or wire is a contained repair compared with replacing a built-in unit. We give a written price before work and cover our repair with a 30-day warranty.