Dometic ProHeat M-Series G-II Temperature Sensor
The Dometic ProHeat 200304K is the factory dual-mode temperature sensor used with G-II PCM ProHeat M-Series diesel-fired coolant heaters.
Unlike the earlier G-I sensor system, the 200304K incorporates both digital and analog temperature-sensing elements into one sensor. ProHeat uses the two signals for normal coolant-temperature control, diagnostic monitoring, and heat-exchanger overheat protection.
Key Features
- Genuine Dometic ProHeat replacement component
- Factory part number 200304K
- Designed specifically for G-II PCM M-Series heaters
- Dual analog and digital sensing elements
- Measures coolant temperature near the heat-exchanger outlet
- Monitors heat-exchanger temperature for overheat protection
- Allows the G-II PCM to compare two temperature signals
- Supports coolant-flow diagnostics
- O-ring included
- Fits multiple standard M-Series heater outputs
- Non-voltage-specific sensor
How the Dual-Mode Sensor Works
The 200304K performs more than one temperature-monitoring function.
The sensor measures coolant temperature near the outlet of the heat exchanger and sends that information to the G-II PCM. At the same time, the sensor contacts the inner heat-exchanger surface so the PCM can monitor heat-exchanger temperature for an overheat condition.
The two internal sensing elements also allow the PCM to compare the analog and digital readings. A disagreement between those readings can indicate a sensor, wiring, or coolant-flow problem.
Normal Temperature Control
The G-II M-Series uses the dual-mode sensor to control normal heater cycling.
During standard operation, ProHeat documentation shows the heater reaching approximately:
185°F (85°C)
before ending full-output combustion and entering its cool-down cycle. During Preheat Mode, the heater can restart when coolant temperature falls below approximately:
160°F (71°C).
Actual behavior can vary with heater mode, PCM configuration, and OEM application.
Overheat Protection
The 200304K also provides heat-exchanger overheat protection.
ProHeat’s G-II service documentation identifies:
Diagnostic Code 4 – Overheat
when the sensor detects an inner heat-exchanger surface temperature of approximately:
257°F (125°C).
An overheat condition should prompt inspection for issues such as:
- Low coolant
- Air trapped in the coolant system
- Restricted coolant flow
- Coolant-pump problems
- Blocked or kinked coolant lines
- Faulty temperature sensor
- G-II PCM temperature-sensor circuit problems
Repeatedly resetting an overheat condition without correcting the cause can damage the heat exchanger.
Diagnostic Code 7 – Temp Sensor / Coolant Flow
The G-II PCM continuously compares the analog and digital sensor signals.
ProHeat identifies:
Diagnostic Code 7 – Temp Sensor/Coolant Flow
This code can indicate one of four conditions:
- Coolant-flow problem causing an analog/digital temperature mismatch
- Analog temperature sensor short circuit
- Analog temperature sensor open circuit
- Digital temperature sensor not communicating with the G-II PCM
Because coolant-flow problems can cause the two sensor readings to disagree, ProHeat recommends checking coolant circulation before automatically replacing the sensor.
Compatibility
The official G-II M-Series documentation covers:
- M50
- M80
- M90
- M105
- M125
The current parts catalog identifies 200304K as the dual-mode temperature sensor for G-II PCM systems only.
G-II Application
The current catalog covers:
G-II PCM model heaters serial 705000 to current, along with heaters equipped with a replacement G-II PCM.
OEM transit-bus and motor-coach configurations may use application-specific control components, so those installations should still be verified.
G-I vs. G-II Sensor
This distinction is important.
PH-200304K
- G-II PCM only
- Dual-mode analog/digital sensor
- Single four-pin temperature-sensor connection
- Current standard M-Series sensor
PH-200302K
- G-I PCM only
- Older overheat/temperature sensor system
- Different PCM and sensor architecture
ProHeat specifically identifies 200304K as the G-II sensor and 200302K as the G-I component. They should not be treated as interchangeable.
O-Ring Included
ProHeat lists 200304K as:
Dual Mode Temperature Sensor c/w O-Ring
The replacement O-ring is:
917724K – Dual-Mode Temperature Sensor O-Ring.
A new sensor therefore already contains the sealing O-ring required for normal replacement.
Installation Notes
When replacing the sensor:
- Allow the heater and coolant system to cool completely
- Isolate the coolant system at the heater inlet and outlet when possible
- Disconnect heater electrical power
- Remove the existing sensor using a 1-inch wrench
- Clean the O-ring and sensor seating surfaces
- Install the supplied O-ring
- Install the sensor until it bottoms against the mounting boss
- Refill and purge the coolant system as necessary
- Inspect for leaks
- Reconnect all G-II PCM harnesses before returning the heater to service
Factory Installation Torque
ProHeat specifies:
100 ± 10 in-lb (11.6 ± 1.1 Nm)
for the G-II dual-mode temperature sensor.
Product Specifications
- BTRAC SKU: PH-200304K
- Manufacturer: Dometic ProHeat
- Manufacturer Part Number: 200304K
- Product Type: Dual-Mode Temperature / Overheat Sensor
- Heater Family: Standard ProHeat M-Series
- PCM Compatibility: G-II Only
- Documented Models: M50 / M80 / M90 / M105 / M125
- Sensor Type: Analog + Digital
- Primary Function: Coolant Temperature Monitoring
- Secondary Function: Heat-Exchanger Overheat Protection
- Overheat Threshold: Approx. 257°F (125°C)
- Temp Sensor Diagnostic: Code 7
- Overheat Diagnostic: Code 4
- O-Ring Included: Yes
- Replacement O-Ring: 917724K
- Installation Torque: 100 ± 10 in-lb (11.6 ± 1.1 Nm)
- Voltage Specific: No
- G-I Compatible: No
Related ProHeat Parts
- PH-917724K – Dual-Mode Temperature Sensor O-Ring
- PH-200302K – Legacy G-I Overheat/Temperature Sensor
- PH-200447K – M-Series Blower Housing
- PH-200419K – M-Series Combustion-Air Blower
- PH-200404K – M-Series 24V Motor
- PH-200508K – M-Series 12V Motor
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