True Refrigeration P3 Error Code — What It Means
P3 on True refrigeration units with Dixell electronic controls signals an auxiliary probe failure. The auxiliary probe monitors a secondary temperature zone or display sensor, and when the control detects an open circuit, short, or out-of-range reading from that probe, it throws P3 and may sound an alarm. On some True models with LAE controls the same condition appears as E3 instead of P3, so always confirm which control family is installed on your cabinet before ordering parts.
The code does not mean the compressor or refrigeration system has failed. It means the control has lost valid temperature data from the auxiliary sensor. The cabinet may continue to cool on the primary evaporator probe, but temperature accuracy and defrost cycles can be affected until the auxiliary probe is repaired or replaced.
Before You Replace Anything
Technicians sometimes replace the electronic control when P3 persists, but a damaged or pinched probe harness or a corroded connector is often the real culprit. Always meter the probe resistance against True’s temperature chart and inspect the wiring path before ordering a new control.
Common Causes
- Failed auxiliary probe (~50%) The sensor itself is open, shorted, or reading outside the control’s acceptable resistance range for the current temperature.
- Damaged or pinched probe wiring (~25%) The harness has been cut, abraded, or pinched against a sharp edge, creating an intermittent open circuit or short to ground.
- Loose or corroded probe connector (~15%) Moisture, grease, or oxidation at the plug prevents a reliable electrical connection between the probe and the control board.
- Wrong probe type installed (~10%) A replacement sensor with the wrong resistance curve was used, so the control reads the temperature as invalid and flags P3.
Quick Diagnosis
Answer these to narrow it down fast.
Is the auxiliary probe connector fully seated and free of corrosion at the control board?
No: Clean the pins with electrical contact cleaner, reseat the plug firmly, and clear the alarm. If P3 returns, continue testing.
Does the probe resistance match True's temperature-to-resistance chart at 32°F or the current cabinet temperature?
No: The probe is out of spec. Replace the auxiliary probe and retest.
After installing a new probe, does the P3 code clear and stay off for a full cooling cycle?
No: Check for a damaged harness or a faulty control board. Call a qualified technician if you cannot find obvious wiring damage.
Step-by-Step Fix
- Identify the control family. Confirm whether your True cabinet uses Dixell or LAE controls by checking the label on the control housing or the model tag inside the cabinet.
- Locate the auxiliary probe. Trace the sensor wire from the control board to the probe mounted in the cabinet, usually near the evaporator coil or on a secondary display sensor location.
- Inspect the connector and harness. Unplug the probe at the control board and examine both the male and female pins for corrosion, bent contacts, or moisture. Look along the entire wire path for cuts, pinches, or abrasion.
- Meter the probe resistance. Using a multimeter set to ohms, measure the resistance across the two probe leads. Consult True’s temperature-to-resistance chart for your model to verify the reading matches the current cabinet temperature.
- Replace the probe if out of spec. If the resistance is open, shorted, or does not match the chart, install a genuine True replacement probe or an exact-match OEM sensor and secure the connector.
- Clear the alarm and test. After reconnecting the new probe, press and hold the alarm-clear button on the control (procedure varies by Dixell model) and monitor the display. The P3 code should disappear and the cabinet should resume normal temperature control.
- Check for return of the fault. Run the cabinet through a full cooling and defrost cycle. If P3 reappears, inspect the harness for intermittent faults or test the control board for internal failure.
Parts Often Needed
| Part | Notes |
|---|---|
| True auxiliary probe (temperature sensor) | Amazon | Match the probe part number to your cabinet model and control type. Resistance curve must match the original. |
| Probe wiring harness | Amazon | Order if the cable is cut, abraded, or the connector housing is cracked. Sold as a complete assembly on many True models. |
When to Call a Pro
Call a qualified commercial refrigeration technician if you are not comfortable working inside energized control panels, if the probe resistance tests good but the P3 code persists, or if you suspect the electronic control board itself has failed. Refrigeration controls operate at line voltage and misdiagnosis can lead to expensive parts replacement. A trained tech will have the exact temperature-to-resistance charts for your True model, the tools to trace intermittent wiring faults, and access to genuine OEM probes and controls that match your cabinet’s specifications.
Rough cost: A pro service call runs about $150–300.