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MODEL OVERVIEW
About this model: GE JTP90SMSS
GE JTP90SMSS combines an upper 1.6-cu-ft microwave with a separate 4.4-cu-ft lower thermal oven. Its official JTP90 guide distinguishes upper SENSOR ERROR from lower F function codes.
Identify the two JTP90SMSS cavities
JTP90SMSS is GE's stainless 30-inch built-in cooking center, with a 1.6-cubic-foot upper microwave and a separate 4.4-cubic-foot lower oven. The exact product specification gives the upper output as 1,000 watts and its turntable as 15.5 inches; it describes the lower cavity as a thermal Bake/Roast oven with self-cleaning. The linked PDF cover names the JTP90 double wall oven family rather than printing the SMSS retail suffix, so the exact GE product page establishes which finish and configuration use this guide. This division matters in troubleshooting: the microwave has its own touch controls, and the lower oven has a second display. The manual even assigns different meanings to an apparently identical 1:30 readout: one minute thirty seconds above versus one hour thirty minutes below. Record which display actually showed a message before treating it as a code for the entire appliance.
Read upper sensor messages in context
The upper sensor controls include Popcorn, Reheat and Potato on the product and in the JTP90 guide. They detect moisture released during cooking, which is why GE specifies microwave-safe containers with a vented cover and dry exterior. With sensor Reheat, steam detection precedes the remaining-time countdown. The troubleshooting table defines SENSOR ERROR narrowly: the microwave door was opened too soon during a sensor function, before the countdown started. A separate Popcorn instruction says opening while POP is displayed produces ERROR. These observations are timing clues, not a diagnosis of a broken electronic sensor. Check the chosen program, food covering and door-opening point before repeating it. Reheat is intended for a covered single serving; the guide instead recommends Time Cook for bread, foods needing stirring, uncovered foods or foods meant to stay crisp.
Choose upper manual and defrost controls
This upper unit also offers a way to cook without relying on the sensor. Time Cook allows a chosen duration up to 99 minutes 59 seconds and lets the power level be changed; GE explains that lower power cycles the microwave energy for gentler or more even heating. Its two-stage Time Cook option can move from one time and power level to another automatically. Auto Defrost is intended for meat, poultry and fish up to six pounds, with TURN prompts to reposition food, whereas Time Defrost is described for other frozen foods. A user who entered no figures after selecting Auto Defrost can see an unresponsive control without having a sensor fault: the troubleshooting chart identifies improperly set controls as a separate problem. Keep the upper turntable and support installed for operation. For a pause during a timed cook, close the upper door and press Start to resume.
Handle the lower oven function code
An F followed by a number or letter is a different JTP90 problem. The guide places it explicitly in the lower oven display and calls it a function error code; it does not supply a universal table translating each F suffix into a replacement part. GE's sequence is to press the lower Clear/Off pad, let that oven cool for one hour and try it again. If the function code repeats, disconnect power to the cooking center for at least 30 seconds and reconnect; call for service if it recurs. This sequence belongs to the lower thermal oven, not the upper SENSOR ERROR response. The lower panel also flashes its clock after a power outage and needs the clock and programmed operations reset. Since the JTP90 has independent controls, note both the exact displayed characters and which cavity was operating when speaking to service.
Separate normal locks and routine care
Several JTP90 display states have ordinary operating explanations. Holding the upper Clear/Off key for about three seconds activates Child Lockout, shown by an L at the far right; the lower oven has a distinct LOC control lock set in its special features. Neither marking means the early-door sensor event. During lower self-clean, LOCKED or LOCKED DOOR remains lit until the cavity cools below the unlocking temperature; trying to force that door would confuse a normal heat interlock with a fault. The 30-inch lower oven has seven rack positions, and the guide cautions against covering an entire rack with foil because it alters heat circulation. For the upper microwave, clean and reseat the removable turntable and support rather than running the cavity without them. These checks help distinguish setup, normal lock and documented diagnostic conditions while preserving the two-cavity distinction.
Verified model details
The stainless 30-inch JTP90 has two distinct cavities and control displays.
Source for this detailAn early upper door opening explains the documented SENSOR ERROR.
Source for this detail · Source page: 39F plus a number or letter belongs to the lower oven and follows a different response.
Source for this detail · Source page: 40
This description summarizes the linked source documents; check each cited source for your exact model and region.
Manufacturer source
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GE® 30" Built-In Double Microwave/Thermal Oven - JTP90SMSS - GE Appliances
Open official sourceIf there is a safety risk, stop using the appliance and follow the manufacturer’s instructions.