Grand Cherokee

NOTE: For circuit identification and wiring diagram, see WIRING DIAGRAMS article. After each repair procedure has been completed, reconnect all components. Perform TEST VER-5 under VERIFICATION TESTS to ensure system is functioning properly.

Start engine and allow it to idle. Allow engine to reach normal operating temperature. Using scan tool, read HO2S states. If HO2S states are switching between RICH and LEAN, system is functioning properly. Test is complete. If any HO2S is not switching between RICH and LEAN, go to next step.
NOTE: 1/2 HO2S and 2/2 HO2S (Calif.) switching should be slower than 1/1 HO2S or 2/1 HO2S (Calif.) switching.
If any HO2S is locked on LEAN, go to next step. If no HO2S is locked on LEAN, go to step 8 .
Ensure engine is still idling. Check engine, brake booster and vacuum hoses for leaks. Repair vacuum leaks as necessary. If no vacuum leaks exist, go to next step.
Ensure engine is still idling. Using scan tool, read HO2S voltages. If voltage is less than .1 volt for any HO2S, go to next step. If voltage is more than .1 volt for all HO2S, turn ignition off and go to step 7 .

Turn ignition off. Disconnect suspect HO2S connector. See HEATED OXYGEN SENSOR LOCATION (GRAND CHEROKEE) table. Disconnect PCM connectors. PCM is located on firewall in right rear corner of engine compartment. Inspect connectors for damaged pins, corrosion and loose terminals. Repair connectors as necessary. If connectors are okay, measure resistance between ground and signal circuit at suspect HO2S connector. See IDENTIFYING HO2S SIGNAL CIRCUITS (GRAND CHEROKEE) table. If resistance is less than 5 ohms, repair short to ground in HO2S signal circuit. If resistance is 5 ohms or more, go to next step.

IDENTIFYING HO2S SIGNAL CIRCUITS (GRAND CHEROKEE)

Application

⁽¹⁾ PCM Terminal (Wire Color)

HO2S 1/1

No. 24 (Light Green/Red)

HO2S 1/2

No. 25 (Black/Dark Green)

HO2S 2/1 ⁽²⁾

No. 26 (Tan/White)

HO2S 2/2 ⁽²⁾

No. 29 (Pink/White)

⁽¹⁾	Terminal is located at PCM C1 connector. See Figure .

⁽²⁾	Applies to Calif. models only.

At this time, suspect HO2S is assumed to be defective. Replace HO2S.

NOTE: 1/2 HO2S and 2/2 HO2S (Calif.) switching should be slower than 1/1 HO2S or 2/1 HO2S (Calif.) switching.

Turn ignition on, with engine off. Using scan tool, reset adaptive fuel memory. Start engine and allow it to idle for at least 3 minutes. Ensure engine is at normal operating temperature. Using scan tool, read HO2S voltage. If HO2S voltage switches normally, no problem is indicated at this time. Test is complete. If HO2S voltage does not switch normally, check engine mechanical condition. See CHECKING ENGINE MECHANICAL SYSTEMS under MECHANICAL INSPECTION in BASIC DIAGNOSTIC PROCEDURES article.

WARNING: Fuel system is under high pressure. Release fuel pressure before disconnecting any fuel lines or fuel system components.

Turn engine off. Release fuel pressure. See FUEL SYSTEM PRESSURE RELEASE under FUEL SYSTEM. Connect fuel pressure gauge to fuel rail. Turn ignition on, with engine off. Using scan tool, actuate fuel system test. Allow fuel pressure to stabilize. Stop fuel system actuation test. Monitor fuel pressure gauge for one minute. If fuel pressure gauge reading drops more than 10 psi (.7 kg/cm² ), fuel pump, fuel lines, injector(s), fuel pressure regulator is defective. To determine defective component, see FUEL SYSTEM PRESSURE LEAK-DOWN TEST under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES article. Repair fuel system as necessary. If fuel pressure does not drop more than 10 psi (.7 kg/cm² ), go to next step.
Turn ignition off. Inspect air cleaner and inlet ducts for restrictions. Repair air cleaner and inlet ducts as necessary. If no restrictions exist, check engine mechanical condition. See CHECKING ENGINE MECHANICAL SYSTEMS under MECHANICAL INSPECTION in BASIC DIAGNOSTIC PROCEDURES article.