Faulty evaporator temperature sensor (internal open circuit); Sensor connector unplugged, loose, corroded or with spread terminals; Open circuit or chafed wiring in the signal or ground wire between sensor and control unit; Signal wire shorted to a voltage supply; Water ingress or damage at the connector after HVAC or dash work; Faulty HVAC or body control module (sensor reference or input circuit).

P1533

A/C Evaporator Temperature Sensor Circuit High Voltage.

GM
Powertrain
Manufacturer code
Low severity

How this code is built

P: SystemPowertrain
1: Defined byThe manufacturer
5: AreaVehicle speed, idle control and auxiliary inputs
33: FaultThe specific fault in that area

What it means

On GM vehicles P1533 means the A/C evaporator temperature sensor circuit is reading high voltage. The control unit sees a signal near the top of its range, which usually points to an open circuit, a poor connection or a failed sensor. With the signal out of range, the A/C system cannot reliably monitor evaporator temperature, so compressor control may be limited.

Symptoms

A/C blows warm or not as cold as it should
A/C compressor does not engage or cycles erratically
Air conditioning warning or A/C light on the dash in some models
Check engine light on
Poor demisting performance if the compressor is inhibited

Possible causes

Faulty evaporator temperature sensor (internal open circuit)likely
Sensor connector unplugged, loose, corroded or with spread terminalslikely
Open circuit or chafed wiring in the signal or ground wire between sensor and control unitlikely
Signal wire shorted to a voltage supplypossible
Water ingress or damage at the connector after HVAC or dash workpossible
Faulty HVAC or body control module (sensor reference or input circuit)rare

How to diagnose

Read all stored codes and freeze frame data, then note any other A/C or HVAC codes before clearing anything
Locate the evaporator temperature sensor for the specific model and inspect its connector and wiring for damage, corrosion or a poor fit
With the ignition on, view the live evaporator temperature value on a scan tool; a reading stuck at the extreme cold or hot end suggests an open circuit
Check the sensor resistance against the manufacturer's temperature table for the model, with the sensor unplugged
Back-probe the connector to check for the reference voltage and a good ground, as specified for the model
Test the signal wire for continuity to the control unit and for a short to voltage, with the battery disconnected where required
If the wiring and sensor are good, check the control unit's power, ground and software status before suspecting the module

How to fix

Replace the evaporator temperature sensor if its resistance is out of specification or it is open circuit
Clean, repair or replace the damaged connector terminals and secure the connector
Repair or replace open, chafed or shorted wiring in the sensor circuit
Dry out and treat water ingress, then replace any corroded connectors
Replace or reprogram the control unit only after the circuit and sensor have been proven good and the manufacturer's procedure confirms a fault

Can I keep driving?

Low severity

The car is safe to drive as the fault affects only the A/C system. Book it in for repair, as the A/C compressor may be disabled until the circuit is fixed.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.