Ωhm

True. Seems like NSS needs some looking at.

Yes. Do your backup lamps work when REVERSE is selected? Page71.

Still using disconnected C234, two (2) voltage tests. KEY ON C234_C9 to D7 when Gear Selector is set to Drive. C234_C8 to D7 when Gear Selector is set to 1 - 2.

True. With C234 disconnected and C114 connected, solenoid continuity can be check for each of your solenoids.

Need to find out why you can't read solenoids values at C114 (Transmission Side).

Technically both ways should have worked, but since were here, disconnect C234 from TCU and probe at the C234 connector. This will help make sure vehicle wiring is GOOD.

Best you can do here is check for voltage at the TCU. C234_D14 - Hot at all times C234_D16 - IGN SW Run/Start

Wonder if low voltage (6vdc) is making for fuel gauge needle not holding true. Might take full battery voltage for fuel gauge to stay more locked in on reading. 2¢

Using battery ground, check D1_5 (Hot at all times) for voltage.

Vacuum line (rubber) about 2’ long. Put your spark plug in one end, find the hole with one hand, insert plug and use other end for twisting hose. Never cross threaded a cylinder or plug. Harder the hole, the easier to do. Once plug is set, pop off hose and tighten to spec.

Is this that fuse? D1_5 - Fuse Link G D2_4 - Ignition Switch (ON/START)

This is what I use for 88-90 MJ's. _mj1988electricalmanual_1.pdf

Thanks for this follow up.

Schematic callout may be wrong. Not the first time I've seen this.

Interesting. I'm using the 88 Electrical Manual. Maybe things changed. Odd.

Truck side. "A" would have battery voltage with KEY ON. "B" will go to ground.

I misled you. Check at the sensor. Didn't realize drawing was for vehicle harness side.

It's internal to the O2S itself. Part of the O2S.

Looks like O2S heater element (A-B) is shorted together internally. No heater.

Key OFF. Disconnect O2S. At the sensor measure ohms between C229_A and C229_B. Look for 5-7 ohms. If good, then signal side of sensor is bad because it's just not switching at idle.

Sound to me like the ECU is doing what it's suppose to do. Open Loop.

Check O2S heater circuit for continuity. Looking for ≈5-7 Ω's.

With that O2 and maybe that Coolant sensor, it can't go into Closed Loop.

O2 (V) seems frozen at idle. Should switch rapidly between 0.5 and 4.5. Rapidly like at the speed of light. Coolant sensor is trashed, or wire is your problem.

O2S with slow response time. O2 is a maintenance item.