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1998 TOYOTA TACOMA
2.7L I4•RWD•AUTOMATIC•gas
5 active safety recalls on this vehicle — view recalls
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Repairs0Labor1038Torque1596Fluid17DTC3336Battery2Maintenance0Recalls5
P0599moderate severityPowertrain

Thermostat Heater Control Circuit High

on 1998 Toyota Tacoma 2.7L I4 · RWD

What this code means

The thermostat heater control circuit voltage is too high. This usually indicates an open circuit or short to voltage in the heater control line.

Symptoms

  • Check engine light on
  • Engine warms up slowly
  • Temperature gauge unstable

Common causes

  • Short to voltage in heater circuit
  • Open in heater control wiring
  • Faulty heated thermostat
  • PCM driver failure

Diagnostic steps

  1. Retrieve stored codes
  2. Check heater circuit for short to power
  3. Verify continuity to PCM
  4. Test thermostat heater command with scanner
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