Camshaft Position (CMP) Sensor
See TESTS W/CODES - 3.9L article in the ENGINE PERFORMANCE section.
Intake Manifold Air Temperature Sensor
Intake manifold air temperature sensor is mounted in intake manifold extending into air stream. Sensor is located at right front of manifold under throttle cable bracket. Turn ignition off, disconnect intake manifold air temperature connector. Using DVOM, measure resistance between sensor terminals. See SENSOR RESISTANCE table. If resistance is not within specification, replace intake manifold air temperature sensor.
Coolant Temperature Sensor (CTS)
- Sensor is located between alternator and A/C compressor.
- With key off, disconnect wire connector from sensor. Connect ohmmeter between sensor terminals. See SENSOR RESISTANCE table. If ohmmeter readings are not within specification, replace CTS.
| Temperature | Ohms |
|---|---|
| 40°F (-40°C) | 291,490-381,710 |
| 4°F (-20°C) | 85,850-108,390 |
| 14°F (-10°C) | 49,250-61,430 |
| 32°F (0°C) | 29,330-35,990 |
| 50°F (10°C) | 17,990-21,810 |
| 68°F (20°C) | 11,370-13,610 |
| 77°F (25°C) | 9120-10,880 |
| 86°F (30°C) | 7370-8750 |
| 104°F (40°C) | 4900-5750 |
| 122°F (50°C) | 3330-3880 |
| 140°F (60°C) | 2310-2670 |
| 158°F (70°C) | 1630-1870 |
| 176°F (80°C) | 1170-1340 |
| 194°F (90°C) | 860-970 |
| 212°F (100°C) | 640-720 |
| 230°F (110°C) | 480-540 |
| 248°F (120°C) | 370-410 |
SENSOR RESISTANCE
Crankshaft Position (CKP) Sensor
- CKP sensor is bolted to cylinder block near rear of right cylinder head, at bellhousing of transmission.
- Disconnect CKP sensor connector from main wiring harness. Measure resistance across CKP sensor wiring connector terminals "B" and "C". (Scheme 88) Replace CKP sensor if any resistance exists.
Scheme 88
Manifold Absolute Pressure (MAP) Sensor
- MAP sensor is connected to side of throttle body by a rubber fitting. NOTE: MAP sensor test must be performed with wiring connector connected.
- Measure MAP sensor output voltage at connector center terminal. With ignition switch in ON position (KOEO), output voltage should be 4.0-5.0 volts. With ignition switch in RUN position (KOER), voltage should be 1.5-2.1 volts. Replace MAP sensor if it fails testing as specified.
Oxygen (O2) Sensor
See TESTS W/CODES - 3.9L article in the ENGINE PERFORMANCE section.
Park/Neutral Position Switch
- Park/neutral position switch is located on transmission. Turn ignition off. Put shift selector in Park position. Disconnect switch harness connector. Using ohmmeter, check continuity between switch center terminal and transmission case.
- If continuity exists, switch is functioning properly. Continuity should also exist in Neutral position. If continuity does not exist, check for correct adjustment. Replace switch if correctly adjusted.
Scheme 89
Transmission Temperature Sensor (CTS)
- On Pickup models (heavy-duty applications) with 4-speed transmissions, sensor is located next to transmission, in-line of cooler line.
- With key off, disconnect wire connector from sensor. Connect ohmmeter between sensor terminals. See «SENSOR RESISTANCE»(ref-10948-S28437776332000111300000) table. If ohmmeter readings are not within specification, replace CTS.
Throttle Position Sensor (TPS)
- TPS is located on throttle body. Disconnect and inspect TPS connector. Repair as necessary. With ignition switch in the ON position, measure output voltage at center terminal (output) wire of connector.
- TPS output should read more than 200 millivolts at idle. At Wide Open Throttle (WOT), TPS output must read less than 4.8 volts.
- Output voltage should increase gradually as throttle is increased from idle to WOT. If voltage readings are not within specification, replace TPS.
Vehicle Speed Sensor (VSS)
VSS is located on transmission extension housing on 2WD models. VSS is located on transfer case on 4WD models. For VSS testing, see TESTS W/CODES - 3.9L article in the ENGINE PERFORMANCE section.
Idle Air Control (IAC) Motor
See TESTS W/CODES - 3.9L article in the ENGINE PERFORMANCE section.
Auto Shutdown (ASD) Relay
- ASD relay is located in engine compartment. Relay terminal numbers are stamped on bottom of relay. Relay must be disconnected for testing. If any of following resistance and continuity tests fail, replace relay.
- Using an ohmmeter, measure resistance between terminals No. 85 and 86. Resistance should be 70-80 ohms.
- Connect ohmmeter between terminals No. 87A and 30. Continuity should exist. Connect ohmmeter between terminals No. 87 and 30. Continuity should not exist.
- Using a pair of jumper wires, connect a jumper wire between terminal No. 85 and battery ground. Connect other jumper wire to battery positive terminal, but DO NOT connect to relay yet. CAUTION: DO NOT allow ohmmeter to contact terminal No. 85 or 86 during following test. Damage to ohmmeter may result.
- Attach other jumper wire to relay terminal No. 86 to activate relay. Continuity should exist between terminals No. 87 and 30, but not between terminals No. 87A and 30. Disconnect jumper wires from battery and relay.
FUEL DELIVERY
Note. For fuel system pressure testing, see the article BASIC TESTING - 3.9L in the ENGINE PERFORMANCE section.
Fuel Injector
Disconnect fuel injector connector. Using a DVOM in ohmmeter position, test between pins of injector for resistance. Resistance should be 13.3-15.7 ohms, replace fuel injector as necessary.
See TESTS W/CODES - 3.9L article in the ENGINE PERFORMANCE section.
IGNITION SYSTEM
Note. For basic ignition checks, see BASIC TESTING - 3.9L article in the ENGINE PERFORMANCE section.
No Air Supply
- Start engine, and raise engine speed to 1500 RPM. Check air supply at rubber hoses. If air supply increases with RPM, air pump operation is okay. If air pump is okay, check for leakage at hoses and fittings. Repair or replace as necessary.
- If hoses are okay, check diverter valve for leakage. If air is expelled through diverter exhaust with vehicle at idle, replace diverter valve. If diverter valve is okay, remove check valve. Blow air through check valve in direction of air pump. Air should not pass through. Blow air through opposite direction. Air should pass freely.
| CAUTION | DO NOT pry on air pump to adjust belt tension; housing may collapse. |
Air Pump
Check and adjust belt tension (if necessary). Disconnect air supply hose from by-pass control valve. Start engine. Pump is operating correctly if airflow is felt at pump outlet and airflow increases as engine speed increases. If pump does not operate as specified, replace pump.
EXHAUST GAS RECIRCULATION (EGR)
Note. To ensure proper EGR system operation all passages and moving parts must be free from restrictive deposits. Clean or replace components as necessary.
EVAP Canister
EVAP canister is located in engine compartment. Canister has no moving parts. Check for loose, missing, cracked or broken connections and parts. Repair or replace as necessary. No Liquid should be in canister.
PCV Valve
- With engine running at curb idle, remove PCV valve from grommet. If valve is functioning properly, a hissing sound will be heard as air passes through valve.
- With engine running, place finger over valve inlet. Strong vacuum should be felt at valve inlet. Stop engine. Remove and shake PCV valve to ensure a metallic clicking noise can be heard, indicating valve is free. Reinstall PCV valve.
- Remove crankcase ventilation filter or oil filler cap from valve cover. Hold a piece of stiff paper over opening. After allowing about one minute for crankcase pressure stabilization, paper should be drawn against opening.
- If paper is held against opening, performance is okay. If paper is not held against opening, replace PCV valve and retest. If performance does not improve, inspect system for restrictions and clean as necessary.
A/C Clutch Relay
See TESTS W/CODES - 3.9L article in the ENGINE PERFORMANCE section.