1990 Geo Tracker Base, AutomaticFACTORY OEM SERVICE PROCEDURE

System Check (A/T)

  1. With engine coolant at approximately room temperature, turn ignition off and disconnect electrical connection at PTC heater, located between throttle body and intake manifold.
  2. Turn ignition on. Using test light connected to ground, backprobe Light Green/Red wire of PTC heater relay connector. Relay is the front relay located at right rear corner of engine compartment, in front of battery.
  3. If no voltage is present, check for open in Light Green/Red wire between relay and control relay. Control relay is located under left side of instrument panel near kick panel and fuse block.
  4. If voltage exists, use test light connected to ground and backprobe White/Black wire of electrical connector at PTC heater relay. If no voltage is present, check for open in White/Black wire between relay and main fuse box 30-amp fusible link. If voltage is present, proceed to step 5).
  5. Turn ignition off. Disconnect coolant temperature sensor located on right side of engine behind coolant hose. Turn ignition on. Using test light connected to ground, backprobe White/Green wire of electrical connector at PTC heater relay.
  6. If no voltage is present, check for open in White/Green wire between relay and ECM Yellow connector terminal No. 10 or faulty ECM. The ECM is located under left side of instrument panel near kick panel.
    NOTE: PTC relay and ECM control wire may be White/Blue on some models. To assist in terminal and wire identification, see appropriate wiring diagram in WIRING DIAGRAMS.
  7. If voltage was present, use test light connected to ground and backprobe PTC heater White/Blue wire of electrical connector at PTC heater relay. If no voltage was present, replace relay. If voltage was present, check for defective connections at relay or defective PTC heater assembly.
Chapter Navigation
Return to Chapter: Positive Temperature Coefficient (PTC) Heater
Factory Service Tools

Use the Manual With the Right Hardware

Pair factory procedures with proven DIY tools so the instructions are easier to execute.

Disclosure: Verified tool recommendations may earn an affiliate commission at no cost to you.

Shop Manual-Ready ToolsCompare Repair QuoteQuote Shield Pro

When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.