00 s80 Bad ECU?

muddblood · Post by **muddblood** » 29 Mar 2015, 14:11

ok...Here is what I have to the best of my knowledge:

- Yellow wire on car harness side of 02 sensor: 83 ohms
- One wire had 130ohms (cannot make out colors)
- Green/Red: 12V (battery voltage). I believe this to be a heater wire as I assume there is a resistor shown in the schmatics.
- I could not locate a 0 ohm wire on the 02 sensor I checked.
- Could not locate a 0 ohm wire on car harness side.

I did check for 0 ohm on another part of the frame so I know I had a good ground. Same point used to check voltage.

I double checked again today and I see 0V (app shows NA) for both front 02 sensors. I'll post freeze frame data if needed.

I could not see a ground wire in the schematics...5 pins go the ECU and one goes to fuse11B/19, which is good and has power. I also am not sure what the B:1 and B:13 reference in the schematics, which seem to go to 2 of the 02 wires.

I also found 2 vacuum leaks, one being at the intake so I fixed both of those (might be the boost sensor and MAF codes)

muddblood · Post by **muddblood** » 29 Mar 2015, 17:57

ECT:
- Red Wire has 5V
- The other wire has 8.1V
- I didn't check the schematics on this sensor, but I figure 2 wires cannot be too hard to check
- The ECT itself has 1330 ohms when cold and I could see the ohms dropping at a consistent pace as the car was running and warming up, so I believe the senor is indeed working.

I also wriggled the harness where the 02's come into, just above the transmission, with all sensors connected, and watched the data stream and nothing changed.

draser · Post by **draser** » 30 Mar 2015, 17:06

So, your front sensors are wide band, so you won't see a voltage for those. Look for AFR on your scanner, and you should read values around 1, more exactly 99.98 to 1.02 for a correctly running engine. You already confirmed you have 12v on pin 3 of front sensor connector, and pin 1 of rear sensor connector. That's supply voltage for sensors heater. The other pin, 4 and 2 respectively, should read 0 with key in pos. 2, ground being made in ECU. You're correct, there's no ground for signal wires either, that we can see, ground being made in ECU as well.
Rear sensors however, are narrow band, and you should be able to read between 0.1 to 0.9 volts right at the sensor, pin 3 and 4 at connector, meter on volts lower scale (1Volt) or auto range.
If you want to measure sensor heater, set meter on ohms and place leads on sensor connector, unplugged, pins 3/4 for wide band and 1/2 for narrow band. Reading should be several tens of ohms for good sensor.
If you want to check a leaky sensor, set meter on ohms, higher scale or auto, pins 4/5 for front, 2/4 for rear. Reading should be nothing, some meters show 1.
If you want to check harness on car side, from sensor to ECU, disconnect battery, unplug ECU, short pins 42/41 on ECU conn (paper clip) then ohm out pins 1/5 at sensor conn, reading should be 0 for good continuity. Same for other wires.
However, in your case, I'd concentrate on ECT circuit. Reason is that your initial reading was -40 degrees, and you need to be able to see 98-100 degrees F for engine to be in closed loop and O2 sensors to work. I see sensor is working from your description. I'd ohm out ECT wires from connector to ECU, like described above. Also, ohm out from ECT connector to chassis to shorts to ground.

draser · Post by **draser** » 30 Mar 2015, 17:07

Correction, engine temp 98-100 Celsius.

muddblood · Post by **muddblood** » 30 Mar 2015, 20:01

I agree that the ECT is probably more import at this point as it controls the fan too. I will check the ECT circuit this weekend (Only have time on weekends to work on it, and weather permitting).

muddblood · Post by **muddblood** » 05 Apr 2015, 11:37

Looks like I will have to wait as I do not have the ECU removal tool. I'll keep you posted.

Oh wait...I figured out a way to get the ECU out. Checking now...

muddblood · Post by **muddblood** » 05 Apr 2015, 12:37

ok...I didn't check the O2 circuit from ECU to the connector...I'm assuming my issue lies in the ECT circuit as it is showing -40 degrees, keeping the car in open loop.

In checking the ECT circuit, the green/red wire from the ECT connector (car side) and pin 4 of the ECU terminal has 0 ohms. The brown black wire (car side harness) leading to pin 60 on the ECU terminal also shows 0 ohms. This confirms that both wires from the ECT connector (car side) to the ECU are in tact. Since the sensor works, am I safe to assume the ECU is indeed bad?

draser · Post by **draser** » 08 Apr 2015, 06:27

Unfortunately you are correct. I'd plug in ECT and read at ECU connector, should read ECT resistance. If ECU connector is clean, no bent or pushed in pins, then...

Post by **precopster** » 08 Apr 2015, 14:53

Do the '99:S80s use a totally different ECT setup to other cars from the same era? This table of values in Celsius covers 1993-2001 ECT values for 850s, S70s & V70s.

0 degrees - 5740 Ohms
10 degrees - 3700 Ohms
20 degrees - 2450 Ohms
40 degrees - 1150 Ohms
80 degrees - 318 Ohms
100 degrees- 184 Ohms

Ohms should decrease as per table but if you start from cold with 13ohms this seems abnormally low.

Always read the ECT value OUT OF CIRCUIT. ie. Not connected to ECU.

muddblood · Post by **muddblood** » 13 Apr 2015, 13:48

So...bad ECU. What options do I have? I know I cannot get a used one and throw it in. Is my best bet here: http://www.volvoecm.com?

00 s80 Bad ECU?

Re: 00 s80 Bad ECU?