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User: For a 1999 Jeep Grand Cherokee Laredo 4.0 V6 that keeps throwing a Code P0352 even after replacing the coil pack, spark…

For a 1999 Jeep Grand Cherokee Laredo 4.0 V6 that keeps throwing a Code P0352 even after replacing the coil pack, spark plugs and fuel injectors, what is the correct troubleshooting order when suspected that the wiring harness is the culprit? Specifically, the harness connector that connects the main engine harness to the actual coil pack, around the back of the engine near the passenger side of the firewall?

Assistant: To help you best, could you confirm a few details:

To help you best, could you confirm a few details:

1. Are you experiencing any specific driveability issues (misfires, rough idle, stalling, etc.)?
2. Have you already visually inspected the harness connector near the firewall for damage or corrosion?
3. Are you looking for a step-by-step electrical diagnostic guide including pinout tests, continuity checks, and ECM signal verification?
4. Do you have access to a multimeter or oscilloscope for testing?

Once I have this, I can give you the most accurate troubleshooting procedure.

User: 1.

1. Rough running
2. No - I need exact precise and step by step iterative instruction
3. Yes
4. I have an endoscopic camera and a multimeter

Assistant: Thanks for confirming.

Thanks for confirming. I’ll gather a detailed, step-by-step troubleshooting procedure specifically for diagnosing a persistent P0352 code on a 1999 Jeep Grand Cherokee Laredo 4.0L (I6 engine) when wiring harness issues are suspected. This will include tests with your multimeter, exact harness connector locations, and instructions for continuity and signal verification.

I’ll update you once the diagnostic guide is ready.

gpt-?

Troubleshooting Code P0352 on a 1999 Jeep Grand Cherokee 4.0L (Wiring Harness Focus)

Background: OBD-II code P0352 indicates an “Ignition Coil B Primary/Secondary Circuit Malfunction” – essentially a fault in the ignition coil circuit for cylinder #2 (coil "B")identifix.comobd-codes.com. In a 4.0L Jeep (inline-6 engine), a coil rail assembly contains three coils (each firing two cylinders). Code P0352 often appears with misfire on cylinder 2 (e.g. P0302) and typically means the Powertrain Control Module (PCM) isn’t seeing the proper current/voltage feedback from the #2 coil circuit. Since you’ve already replaced the coil pack, spark plugs, and injectors, the wiring harness (or its connectors) is a likely culpritobd-codes.com. Below is a step-by-step troubleshooting guide focusing on the harness connector at the back of the engine (near the passenger-side firewall) which links the main engine harness to the coil pack.

Tools and Preparation

• Safety: Park on a level surface, engine off, and disconnect the battery before probing wires (to avoid shorts). Reconnect the battery only when instructed (for live voltage tests or running tests).
• Tools Needed: A good flashlight and your endoscopic camera (to see behind the engine), plus a multimeter (for voltage and continuity checks). Having electrical contact cleaner and some basic hand tools (for accessing connectors and removing loom tape) is also recommended.

Step-by-Step Troubleshooting Guide

1. Inspect the Coil Pack Harness Connector (Visual Check): Locate the ignition coil pack’s wiring connector at the rear of the engine (passenger side, near the firewall). This is the junction between the coil rail and the main harnesswranglertjforum.com. Ensure the battery is disconnected, then unplug the connector from the coil pack. Use your endoscopic camera or a mirror to closely inspect the connector and wiring: - Connector Condition: Check for any corrosion on the pins, moisture, dirt, or burnt spots. Also see if the plastic housing or locking tab is cracked or broken (a loose or broken connector lock can cause a poor connection)obd-codes.com. - Wires at Connector: Examine the wires where they enter the connector – look for frayed insulation, exposed copper, or kinks. This area can be stressed due to engine vibration and heat. - Clean and Reseat: Spray electrical contact cleaner on both the male and female connector pins to remove oxidationwranglertjforum.com. Let it dry, then plug the connector back in firmly until it clicks. Make sure it’s fully seated; a half-connected coil plug will definitely trigger P0352.
2. Perform a Wiring “Wiggle Test”: Reconnect the battery and start the engine (or at least turn the ignition to RUN if the engine won’t stay running). With the coil harness connector plugged in securely, wiggle the wiring harness section going to the coil pack – especially the portion right at the connector and the length of harness that runs behind the cylinder head. Do this with care (watch out for moving parts if the engine is running). Observe the engine and code reader: - If wiggling the harness causes the engine to stumble, miss, or triggers the P0352 code immediately, that strongly indicates a wiring issue or loose connection in that areaobd-codes.com. You may literally see the misfire occur as you manipulate the wires, confirming a faulty wire/connection. - If nothing changes during the wiggle test (no new misfire induced), the fault may not be a simple loose connection. Continue to the next steps for deeper electrical testing. (Intermittent problems might only show up when the engine vibrates or under certain conditions, so wiggle thoroughly along the harness route to be sure.)
3. Check the Coil Pack Power Supply Circuit: Turn the ignition off again. Using your multimeter, identify the power feed wire for the coil pack at the connector. (On Jeep 4.0 coil rails, typically one wire supplies +12V from the ASD relay/fuse, and the other wires are control signals from the PCMobd-codes.com.) Now, turn the ignition ON (engine off) and measure the voltage on the coil pack’s power wire: - You should see roughly battery voltage (~12V) on the coil’s common feed wireobd-codes.com. If you do, the power supply from the fuse and ASD relay is OK. - No Voltage? If there is 0V at the coil connector’s feed, you likely have a blown fuse or ASD relay issue. Check the under-hood Power Distribution Center (PDC) for the ignition coil fuse (for example, Fuse 18 on some models feeds the coil/ASD)wranglertjforum.com. Replace any blown fuse only after inspecting for a short in the harness (a blown fuse indicates a possible short-to-ground in the coil power circuit). Also swap or test the ASD relay if necessary. Ensure power is restored to the coil connector before proceeding.
4. Test the Coil “B” Control Wire Continuity: P0352 points to the coil “B” circuit (cylinder #2’s coil). The coil pack connector will have a specific pin for the coil B trigger wire (consult a wiring diagram if available – coil B might correspond to the second coil in the rail, firing cyl 2 & 5). Now, check the integrity of that control wire from end to end: - Preparation: Ignition off, battery disconnected. Unplug the coil pack connector again. Also disconnect the PCM connector (to avoid damaging the PCM or getting false readings). Find the PCM pin that corresponds to the coil B driver (in a ’99 Grand Cherokee 4.0, the PCM has separate pins for coil drivers A, B, C). - Continuity Test: Use the multimeter in resistance (ohms) mode. Probe the coil B control wire at the coil connector and the corresponding PCM pin. A good wire should show very low resistance (near 0 Ω). Wiggle the harness while measuring – the reading should remain steady. - Result: If the multimeter shows infinite resistance/open circuit, that wire is broken between the PCM and coil connectorobd-codes.com. A partially broken wire might show intermittent continuity if you flex the harness. Repair any open by splicing in a new wire section or repairing the connector pin as needed, then re-check continuity (solder and heat-shrink tubing or a weatherproof crimp connector are best for durability). - If continuity is good (a steady low resistance), the wire is at least intact. In that case, the issue could be an intermittent short or a PCM driver problem – proceed to the next check.
5. Check for Shorts to Ground or Voltage: With the coil and PCM still unplugged, use the multimeter to check if the coil B control wire is shorted to either ground or a voltage source: - Short to Ground Test: Set the meter to ohms and measure between the coil B wire (harness side) and a good engine ground. You should get no reading (∞ ohms) – meaning the wire is not touching ground. If you read a low resistance (anything other than open circuit), that indicates the wire’s insulation may be compromised and touching ground (metal engine/transmission, etc.)obd-codes.com. You’ll need to find where the wire is grounded (look for crushed sections or burnt spots where it might contact the engine) and fix the insulation or replace that segment. - Short to Power Test: Next, check resistance between the coil B control wire and the 12V feed wire in the same harness. Again, you expect ∞ ohms (no continuity). If the coil driver wire shows continuity to a hot 12V source, it’s likely melted to another wire that carries powerobd-codes.com. Inspect the harness for any melted-together wires. Pay attention to where the harness might run near hot exhaust or sharp edges which could cause such damage. Repair any identified short (separate the wires and fix insulation). - Repair Verification: If you found and repaired any shorts, repeat the continuity tests above to ensure the coil B wire is now only connected where it should be (to the PCM pin and nowhere else). This harness circuit must have a single, clean path from the PCM to the coil pack with no unintentional grounding or power contact.
6. Thoroughly Inspect the Harness Routing: If continuity and short tests didn’t pinpoint the issue, perform a meticulous physical inspection of the harness segment in question. The coil wiring harness on the 4.0L runs from the coil connector behind the engine, across the back of the valve cover, and over to the PCM (near the firewall). Use your endoscopic camera to look at hard-to-see sections: - Remove Loom/Tape: Gently open up any plastic loom or electrical tape wrapping this part of the harnessjustanswer.com. Often problems hide inside the loom. Look for discolored insulation, squished wires, or any green corrosion on copper strands. - Common Chafe Points: The harness bend behind the cylinder head (near the A/C lines and firewall) is a known trouble spotjustanswer.com. Check if the harness was rubbing against the engine, firewall, or A/C tube – any sharp metal edge can chafe through insulation over time. Also inspect where the harness ties into the main loom; sometimes zip-ties or brackets pinch wires. - Repair as Needed: If you discover any damaged wire, repair it (or replace that section). For any minor insulation damage, you can use high-quality electrical tape or heat-shrink tubing. For major cuts or corrosion, splice in new wire of the same gauge and seal it properly. Take your time to ensure no stray wire strands short to anything else. After fixing, re-wrap the harness with loom/tape to protect it. - Connector Condition: If the coil pack connector itself is damaged (cracked housing, loose pins that won’t make good contact, etc.), you may need to replace it. Fortunately, replacement pigtail connectors are available for the Jeep 4.0 (with pre-attached wires you splice into the harness).

Example of a 4-wire ignition coil connector pigtail for Jeep 4.0L. If your harness connector is beyond salvage (broken lock tab or heavily corroded pins), installing a new connector pigtail ensures a solid connection. Splice each wire from the new pigtail to the corresponding harness wire (use solder or quality crimp connectors with heat shrink). A secure, weather-tight connector will eliminate many intermittent coil circuit issues.

1. Re-test the Circuit and Clear Codes: After any repairs, reconnect all connectors (coil pack, PCM, etc.) and reconnect the battery. Double-check that the coil pack connector is firmly attached. Now, clear the fault codes (with an OBD-II scanner or by disconnecting the battery for a few minutes). Start the engine and monitor performance: - Initial Start: The engine should run smoother if the misfire source was fixed. Drive for a short while and see if the Check Engine Light comes back on. A successful repair means P0352 stays gone and cylinder 2 misfire is resolved. - If Code Returns: If P0352 reappears or the engine still runs rough, we need to verify if the coil is receiving a trigger from the PCM. Using your multimeter, you can do a signal test: disconnect the coil connector again while the engine is off. Start the engine (it will run on fewer cylinders). Measure AC frequency (Hz) between the PCM’s coil B driver wire and ground – many multimeters have a frequency setting. You should see a reading in the ballpark of 5–20 Hz at idle if the PCM is pulsing that coil outputobd-codes.com. (Alternatively, an LED test-light between the coil driver pin and battery positive can blink, indicating pulses.) - If you do detect a pulse from the PCM (frequency present or test-light blinks), that means the PCM is trying to fire the coil. In that case, suspect the coil pack assembly again – even new parts can fail. Also double-check the spark plug and injector for cylinder 2 (since a continued miss could be fuel or compression related, though those typically throw different codes). - If you do NOT see any trigger signal from the PCM on the coil B circuit (no frequency, no pulsing voltage) even after all wiring fixes, then the PCM’s coil driver might be faultyobd-codes.com. A final confirmation would be that all wiring from PCM to coil is now verified good (steps above), and yet coil B never gets a signal. PCM failure is less common, but it can happen – especially if a wiring short overloaded that driver. In this scenario, replacing the PCM could be required. (Before condemning the PCM, you might swap the coil trigger wires for coil B and another coil at the PCM connector – only if comfortable – to see if the misfire moves, but this is advanced and generally not necessary if all other tests point to PCM.)
2. Additional Notes: In rare cases, mechanical issues can cause what appears to be an ignition circuit code. For example, one known issue on Jeep 4.0s is excessive wear in the camshaft position sensor drive (oil pump drive) causing timing issues and false misfire codesjustanswer.com. However, P0352 is most often an electrical problem – damaged wiring, poor connections, or a failing PCM driver. Since you focused on the harness connector (a common failure point) and performed the above tests, you have addressed the likely causes. Always finish by securing the harness away from hot or moving parts (use zip ties or loom holders to prevent future chafing) and ensure all connectors are tight. With the wiring issue resolved, your Grand Cherokee should no longer throw P0352 and will resume smooth running on all six cylinders.

Sources

• Identifix, Code P0352: The Diagnostic and Repair Guide – Explains the meaning of P0352 and general diagnostic stepsidentifix.comobd-codes.comobd-codes.com.
• Wrangler TJ Forum – User advice for P0352/P0302 on Jeep 4.0L: check the coil harness connector at the back of the engine, clean/inspect it, and look for wiring damagewranglertjforum.com.
• OBD-Codes.com – Diagnostic steps for P0352: includes performing a wiggle test on the wiring harness, checking for loose connections, and how to test the coil driver circuit with a multimeterobd-codes.comobd-codes.com.
• JustAnswer – Jeep Tech – Noted common P0352 causes: wiring harness damage behind cylinder head (near A/C line) and an unrelated cam/oil pump drive issuejustanswer.com.
• Jeep Wrangler/TJ Forum – Guidance on checking power supply (fuse/relay) for coil pack (Fuse 18 from PDC to ASD to coil in similar Jeep models)wranglertjforum.com.