OK guys, here's the problem I've been having. My 89 4WD 22RE keeps setting the notorious code 25/26 (Too Lean/Too Rich)

So I checked for vacuum leaks with a smoke machine (none), checked injector resistance, replaced the coolant temp sensor, all to no avail.

I decided to check what kind of voltage my 02 sensor was putting out. Hooked up the multimeter to the "Ox" test port on the diagnostic check connector by the fuse box, and got nothing, 0v. So off came the pass kick panel, and I checked it directly at the ECU (Connector 2, Pin 13, black wire). Same thing, no signal from the 02 sensor. I went under the truck, unplugged the 02 sensor, grabbed a wiring diagram, set the multimeter to continuity and began checking connections.

Here's the wiring diagram:



At The 02 Sensor
Pin.......Circuit Name.......Circuit Type...........Wire..........Pin at ECU....Color on Diagram
1..........HT1..................Heater............ ......Pnk-Grn.....C2P15..........Pink
2..........B+....................Battery Positive......Wht-Rd.....C1P1............Red
3..........OX1..................O2 Signal...............Blk...........C2P13.......... Green
4..........E1....................Ground (Earth)........Brn...........C3P7............Blue

So I have a good connection on all four wires from the 02 sensor to the ECU
When running, I have a good ground on C3P7, a good power on C1P1, and I'm assuming that the HT1 wire should be the ground for the heater circuit?

The 02 sensors I've been putting in are all Bosch units. Bosch uses two white wires for the heater, a gray wire for the ground, and a black wire for the signal. So here's how I've been wiring it:

OEM Wire............Bosch Wire
Pnk-Grn..............White
Wht-Rd..............White
OX1...................Black
E1.....................Gray

Any ideas? I've put 3 sensors in it now, the original one, and two new ones, and not one of them gives me a signal back to the ECU. Any ideas would be appreciated.

Dirk

 

I cant say why you aren't getting signal, but I can tell you Bosch o2 sensors do not play nice with Denso electronics. Rule of thumb, never use Bosch sensors on your yota. Relays are a different story.

 

OK, I just had a heck of a busy weekend, but I did get this figured out friday afternoon, and figured I should post the results in case they're useful to someone else down the road....

I got my hands on an NTK sensor and had the same issue. So i unplugged the sensor, and probed it while it was unplugged. Then the sensor was putting out voltage, but it would drop to 3.4 mV every time i plugged it back in.

I unplugged it again and checked resistance to ground on the Ox circuit (black wire), and discovered it was 0.2 ohms. My first thought was a bad/shorted ECU, so I unplugged the ECU and checked the wire again. Still shorted to ground.

So somehow, somewhere, my 02 signal wire shorted to ground. I got a new shielded wire from the parts store and wired Pin 3 on the 02 sensor straight to C2P13 at the ECU. I ran the wire through the waterproof grommet under the passenger seat, and wrapped it in loom so it wouldn't rub on anything.