mypros+
Error code reference

Bosch Microwave Error Code H99

Self-diagnostic failure code indicating a magnetron and/or inverter circuit problem area; no microwave…

Bosch codesBosch microwave codes

Self-diagnostic failure code indicating a magnetron and/or inverter circuit problem area; no microwave oscillation detected.

First step from the service manual

Program DPC by pressing Clock, Timer, Start, Power Level. Then perform inverter Test1: unplug CN703 from magnetron, program High power for 1 minute, verify oven stops in ~23 seconds and input current is 0.5-1A.

The complete diagnostic procedure includes additional test steps, resistance specifications, wiring diagram references, and component test points.

MyPros+ Max

Get the full diagnostic procedure for H99.

  • Step-by-step tests with expected resistance, voltage, and continuity values
  • Wiring diagram references and connector pinouts from the OEM service manual
  • Verified part numbers when replacement is required
Get the full procedure

$29/month · Cancel anytime · Or $9.95 3-day pass

What H99 means on a Bosch microwave

The H99 error code on a Bosch microwave is a self-diagnostic failure code that signals a problem in the magnetron or inverter circuit, specifically that no microwave oscillation has been detected during operation. The inverter circuit is responsible for converting incoming AC power into the high-frequency, high-voltage energy required to drive the magnetron. When the control system initiates a cooking cycle and fails to confirm that the magnetron is producing microwave energy, it throws H99 and halts operation to prevent damage to the unit.

The diagnostic process for H99 begins with programming the DPC (digital power controller) using the key sequence: Clock, Timer, Start, Power Level. After this initialization, the technician runs Inverter Test1 by unplugging connector CN703 from the magnetron, setting the oven to High power for one minute. A properly functioning inverter will cause the oven to shut down in approximately 23 seconds with an input current reading between 0.5 and 1 amp. This test isolates the inverter from the magnetron, allowing the technician to determine whether the fault lies in the inverter circuit itself or in the magnetron and its associated wiring.

Common causes of H99 include a failed magnetron, a defective inverter board, a wiring fault at connector CN703, or an open magnetron filament. Because high-voltage components are involved, this error code should be treated as a serious fault requiring careful, systematic diagnosis. Technicians must discharge the high-voltage capacitor before probing any part of the inverter or magnetron circuit.

Source: manufacturer service documentation.

Common causes of H99

  1. 01

    Failed magnetron

    Part replacement

    The magnetron is the component that generates microwave radiation. If its filament is open or the tube has failed, the inverter will receive no load feedback and H99 will be triggered.

  2. 02

    Defective inverter board

    Part replacement

    The inverter board converts line voltage to the high-frequency power needed by the magnetron. A faulty inverter will fail to produce the correct output even if the magnetron is intact, and Inverter Test1 using CN703 is used to isolate this component.

  3. 03

    Loose or damaged CN703 connector

    Wiring / connection

    The CN703 connector links the inverter circuit to the magnetron. A loose, corroded, or broken connection at this point can interrupt the signal path and prevent oscillation from being detected.

  4. 04

    Open magnetron filament circuit

    Wiring / connection

    If the filament wiring between the inverter and the magnetron is broken or has high resistance, the magnetron will not heat up and no oscillation will occur, resulting in H99.

  5. 05

    DPC programming error or control board fault

    Wiring / connection

    If the digital power controller has not been properly initialized or has developed a fault, it may incorrectly report no oscillation even when the inverter and magnetron are functional. Re-programming the DPC with the Clock, Timer, Start, Power Level sequence is the first step in ruling this out.

See the test procedure for each cause

Frequently asked questions about H99

What does H99 mean on a Bosch microwave?
H99 is a self-diagnostic failure code indicating that the microwave detected no oscillation from the magnetron or inverter circuit during operation. The control system monitors whether the magnetron is actually generating microwave energy, and when it cannot confirm this, it logs H99 and shuts the oven down. This points to a problem somewhere in the high-voltage power chain that drives the magnetron.
Can I fix the H99 error myself?
Diagnosing H99 requires working near high-voltage components including the inverter board and magnetron, which retain dangerous charge even after the unit is unplugged. The proper first step is programming the DPC and running Inverter Test1 by disconnecting CN703, which requires a current measurement and knowledge of safe capacitor discharge procedures. Most homeowners should leave this repair to a qualified appliance technician. If you are comfortable with high-voltage electronics, follow the structured test sequence precisely before touching any components.
Is it safe to use my Bosch microwave when it shows H99?
No, you should not continue using the microwave while H99 is active. The code indicates the oven has detected a failure in the magnetron or inverter circuit and has shut down cooking as a protective measure. Attempting to force the oven to operate in this condition could cause further damage to the inverter board or magnetron, and high-voltage components inside the unit remain hazardous even when the oven is not actively running.
Will resetting the microwave clear the H99 code?
A simple power reset is unlikely to permanently clear H99 because the code reflects an actual hardware condition, specifically the absence of detected microwave oscillation. The code may temporarily disappear after a reset, but it will return as soon as the oven attempts another cook cycle and again fails to detect magnetron output. Clearing H99 permanently requires identifying and correcting the underlying fault in the magnetron, inverter, or CN703 wiring.
How much does it cost to repair a Bosch microwave showing H99?
Repair costs vary depending on which component has failed. A magnetron replacement typically runs between $150 and $350 including parts and labor, while an inverter board replacement can range from $120 to $300. If the fault is only a damaged or loose CN703 connector, the repair cost may be significantly lower. For higher-end built-in Bosch models, total repair costs including diagnostic fees can reach $400 or more, at which point comparing repair cost to unit replacement value is worth considering.

Related Bosch microwave codes

All Bosch microwave codes

78,000+ service manuals · 160,000+ error codes · 55+ brands

Get Started

$29/month · Cancel anytime · Or $9.95 3-day pass