The 2.4L inline-four variant in Chrysler’s early-2000s compact utilizes a dual-stage temperature regulation assembly requiring precise relay sequencing. Locate the primary speed control module adjacent to the radiator support–marked C215 on schematics–where power feed splits into low and high circuits. A 30A fuse (position 8 in the under-hood distribution panel) protects the main input; verify continuity before proceeding.
Trace the dark green/light blue harness bundle to pin 87 of the fan control relay–this triggers the secondary stage when engine temps exceed 107°C. For low-speed operation, a separate purple/yellow lead connects to pin 85, energized through the powertrain control module at 98°C. Ground paths converge at chassis point G103; corrosion here mimics relay failure.
Testing requires a digital multimeter set to 20VDC. Backprobe connector C215 while monitoring voltage drop during simulated heat-soak conditions. Expected readings: 13.2–14.1V at low speed, 11.8–12.5V under load. Deviations below 11V indicate parasitic draw–isolate circuits individually using a fused jumper wire.
Replace the thermal sensor cluster if response lag exceeds 3 seconds at operating temperature. The NTC-type probe (part #56041290AA) threads into the thermostat housing; specify 75Wx16mm thread pitch. Recalibrate the ECM post-installation via OBD-II reset procedure “IMPLAUSIBLE SIGNAL”.
PT Compact Electrical Ventilation Circuit Layout
Locate the primary relay beneath the dashboard on the driver’s side–marked by a black box with a 30A fuse–before proceeding. Disconnect the battery’s negative terminal to prevent accidental shorts while handling connectors. The system relies on two speed settings: low and high, controlled by separate relays. Low-speed operation engages via the radiator temperature sensor, typically closing the circuit at 210°F (99°C). High-speed activation occurs at 230°F (110°C), triggered by the powertrain control module (PCM) signals sent to the secondary relay.
Inspect the motor’s wiring harness for color-coded leads:
- Dark green/white stripe: High-speed power input (connected to the PCM relay).
- Tan/black stripe: Low-speed input (fused directly from the battery).
- Black: Ground connection (bolted to the chassis near the front bumper).
- Light blue/red stripe: Sensor feedback wire (links to the PCM for temperature monitoring).
Corrosion on these terminals often causes intermittent failures; clean with electrical contact cleaner and apply dielectric grease during reassembly.
Test relay functionality using a multimeter:
- Set to continuity mode. Probe pins 85 and 86–should register closed when energized.
- Measure voltage between pin 30 and ground–12V DC must present when ignition is on.
- Check pin 87 for output voltage–absence indicates a faulty relay or blown fuse (check both 30A fuses in the under-hood box).
Replace relays exhibiting resistance outside 50–120 ohms or voltage drops exceeding 0.5V across contacts.
For aftermarket upgrades, prioritize OEM-spec components–aftermarket relays often lack thermal protection, risking premature failure under sustained 20A loads. If installing a dual-fan setup, splice the secondary motor’s power lead directly to the high-speed circuit, ensuring the added draw does not exceed the factory 30A fuse rating. Use 10-gauge wire for all modifications to prevent voltage sag under load.
Common failure points include:
- The temperature sensor’s plastic housing–cracking leads to coolant seepage into the connector, causing shorts.
- The ground strap near the front bumper–vibration loosens the bolt, creating a high-resistance path.
- The PCM’s signal wire (light blue/red stripe)–mice often chew this during winter storage; route through conduit if replacing.
Always verify repairs by monitoring actual motor engagement–spinning blades confirm the circuit is intact, but lack of air movement may indicate a seized motor despite correct wiring.
Locating the Engine Temperature Control Relay and Fuse Positions
Check the under-hood fuse block near the battery–relay R5 (labeled “Radiator Support Fan”) sits in slot 3, while R12 (“AC Condenser Fan”) occupies slot 4. Fuses F35 (30A) and F40 (20A) share the lower row; probe with a test light to confirm power at terminals 30 and 87 when ignition is on. If voltage is absent, verify fuse integrity by prying out each blade with needle-nose pliers–replace cracked or corroded units immediately.
For the interior fuse panel, remove the driver’s side kick panel by unscrewing two 7mm bolts. Identify F14 (10A, “Engine Control”) in position 14–this powers the signal feed to both relays. Use a multimeter set to continuity mode; probe between relay socket terminal 86 and ground–absence of beep indicates a broken wire or faulty ECM output. Label each connection before disconnecting to avoid cross-wiring during reassembly.
Step-by-Step Wire Color Coding and Terminal Connections
Identify the harness connector on the motor assembly–it uses a 2-pin plug. Pin 1 (black/light green tracer) carries ground; pin 2 (dark green/white tracer) supplies 12V switched power. Strip 5 mm of insulation from each lead, then crimp a female spade terminal rated for 18 AWG wire. Verify continuity with a multimeter before connecting to prevent reverse polarity.
Use the table below to match factory wiring colors to aftermarket relays or controllers. Measure voltage at the vehicle’s fuse box under the dash: terminal 30 outputs constant 12V, terminal 87 outputs fused power only when the ignition is ON, terminal 85 connects to the engine temperature sensor signal, and terminal 86 bridges to ground.
| Wire Color | Factory Function | Terminal | Recommended Gauge |
|---|---|---|---|
| Dark green/white | Switched 12V | 87 | 16 AWG |
| Black/light green | Ground | 85 or chassis | 14 AWG |
| Yellow/red | Sensor signal | 86 | 18 AWG |
| Red/dark blue | Constant 12V | 30 | 12 AWG |
Label each wire with heat-shrink tubing before routing through the firewall grommet–left side near the brake master cylinder. Secure the relay to the inner fender using a grounded bolt; avoid plastic mounts to prevent voltage drop. Test operation by running the engine to operating temperature: the assembly should engage within 3–5 seconds of reaching 195°F. If delayed, inspect the relay coil resistance (should read 70–90 ohms) and sensor resistance (should drop below 200 ohms at 212°F).
Troubleshooting Reverse Polarity
If the motor spins backward, swap the dark green/white and black/light green wires at the harness connector. Confirm correct rotation by observing airflow direction–it must push air toward the radiator, not pull. Replace any corroded terminals with gold-plated connectors to ensure consistent current flow.
Verifying the Engine Airflow Module’s Voltage Input
Disconnect the module’s electrical connector and set a multimeter to DC voltage (20V range). Probe the harness terminals while an assistant activates the climate control at its highest setting: the blower must remain off. Terminal A (labeled “B+”) should read battery voltage (13.5–14.2 V) within 2 seconds; Terminal B (“Signal”) must swing between 0.5 V (low) and 4.8 V (high) within the same interval. Any deviation outside these thresholds confirms a defective relay, blown fuse #17 (30 A), or a severed feed line from the under-hood fuse box.
Ground Circuit Integrity
Attach the multimeter’s black lead to a known chassis ground and the red lead to Terminal C (ground return). With the ignition on but the motor unenergized, voltage should not exceed 0.1 V. A reading above 0.3 V indicates corroded ground strap G103 behind the left-front strut tower; clean both contact surfaces with a stainless-steel brush and apply dielectric grease rated for 250 °C. Recheck voltage: if still above 0.3 V, the ECU ground plane inside the cabin fuse block is compromised–remove the instrument panel lower trim to inspect the G200 stud.
Use a 10 A fused jumper wire to bridge Terminal A directly to Terminal C; the module should spin at full speed without hesitation. No rotation signifies internal brush wear or a seized rotor: replace the assembly. Spinning with a rough sound or slower than 3,200 rpm (±200) at 14 V signals worn bearings–verify bearing play by lifting the rotor shaft; end play >0.3 mm mandates immediate replacement.
After reinstalling connectors, monitor voltage drop across Terminals A–C under load: drop should stay under 0.2 V. Exceeding 0.5 V at 2,800 rpm reveals undersized wires (harness section AWG 14 is minimal) or loose crimps at splice S112 near the radiator support–repair with gold-plated butt connectors and heat-shrink tubing rated to 125 °C.
Tracing the Low-Speed and High-Speed Ventilation Circuit Paths
Begin by locating the dual thermal sensors–one positioned near the upper radiator hose (yellow connector, two-pin) and the second adjacent to the lower hose (black connector, single-pin). The first activates the low-speed relay (R31, grey 15-amp) when the coolant reaches 93°C (200°F), while the latter triggers the high-speed relay (R32, brown 30-amp) at 104°C (220°F). Probe terminals 85 and 86 on each relay with a multimeter set to continuity mode; a reading below 0.5 ohms confirms a functional coil. If resistance exceeds 1.5 ohms, replace the relay immediately–hindering airflow at elevated temperatures risks engine seizure within 6-8 minutes of sustained operation.
Key Circuit Landmarks
- Battery Feed: Both relays draw power from fuse #24 (40A) via a 10-gauge red wire terminating at the under-hood fusebox (terminal 30). Verify voltage at this junction before proceeding–no power here disables the entire system.
- Controller Module: The PCM (Powertrain Control Module) governs the low-speed circuit via a dark blue/white wire (pin 32 on connector C2) and the high-speed via a tan/yellow wire (pin 33). Use a scan tool to monitor PIDs ECT (Engine Coolant Temp) and FAN RELAY COMMAND; discrepancies indicate PCM corruption or a severed signal wire.
- Ground Path: Both motors share a body-ground (G103) near the left strut tower. Scrape paint from the mounting surface and ensure the black 12-gauge wire crimps securely–corrosion here mimics relay failure, causing erratic activation.
- Motor Resistance: The low-speed winding should read 0.8–1.2 ohms, while the high-speed winding measures 1.5–2.0 ohms. Readings outside this range demand replacement; no aftermarket substitutions meet OEM torque specifications (3.5 Nm for the mounting bolts).
Route a 16-gauge test lead from the positive battery terminal to the motor’s high-speed terminal (bypassing the relay). If the motor spins, the relay or PCM is faulty. If silent, the motor’s brush assembly is compromised–disassemble and inspect the commutator for copper oxide deposits, a common failure point after 80,000 miles. Rotate the impeller by hand; detectable resistance suggests bearing seizure or foreign debris lodged in the housing.