355 Code P1448 Every 50 Miles

I don't think he understands the problem you have. The exposed wire is on the non-black/white/grey side of the connector. If the problem is there, the fuse will blow irrespective of how many O2 sensors you have plugged in. He's also suggesting what we don't want you to do.

Whilst it is probably the damaged insulation causing the problem, we just want you to eliminate other causes before you start reinserting fuses.

 

Not sure what to make of this. There will be some kind of earth in the Motronics ECU. There may be a direct connection from the ECU to the car (completing the loop) or, more likely, there may be some electronics in the ECU as part of that loop. The electronics may not like you measuring the resistance of the circuit. When you measure resistance, the meter puts a small current into the circuit.

What display do you get on your meter when the leads are not touching anything (in resistance mode). Does it show "0L"? This means open circuit (infinite resistance). When you say the meter does nothing on one wire, does it continue to show the same indication that you got with the leads connected to nothing? That should be the power wire from the fuse. The one that flashed is probably the wire going to the ECU. Is the same behaviour repeated for the other sensors?

Possibly. Driving without an O2 sensor hooked up may be telling the ECU to pump lots of extra fuel into one bank and your cat will be overheating and suffering as a result. I would reconnect the O2 sensor you disconnected.

If you do decide to go on another drive (assuming you've patched up the wiring properly and hooked up the O2 sensor), the SD light may go away completely, but I wouldn't immediately panic if it comes back. The false O2 sensor information which has been going to the ECU (courtesy of the shorted wiring or disconnected O2 sensor), may take a certain time period to be un-learnt (?) Of course, if the problem continues, I would take the car to your mechanic.

Regarding your meter. After this problem has gone away, I would remove the battery from your meter. You don't know when your next electrical problem will happen, and batteries have a tendency of leaking and destroying the meter battery contacts.

 

The 1 may actually be a lower case "L" (open circuit).

 

Hopefully your mechanic will have nothing to do

 

I don't know if the codes are old or not, but:
p1119, p1115 are left and right O2 heater related
p0154 is "no activity detected" on left upstream cat. Was that the O2 sensor you left disconnected?

p1445 is related to the slow down light (I think the right hand bank). According to the manual, may be:
Faulty thermocouple, faulty thermocouple ECU, problem related to injectors or ignitors, fuel tank level (????).

 

Did your fuse blow again?

Perhaps the light is showing a real cat overheat problem or the SDECU is over-reading. An infra-red temperature gun should tell you or your mechanic if the heat problem is real.

 

If it started flashing almost immediately, then your cat should be ok. It wouldn't have had time to heat up that fast. It has to be a thermocouple, SDECU or wiring.

If you had more time, you could have swapped SDECU's to see if the problem transferred to the other bank. Your message would become P1454

Technistrada offer some cheaper SDECU's and thermocouples. Note: I don't know if you're looking for originality, but their SDECU is somewhat smaller and lighter than OEM.

https://technistrada.com/

 

Green helps, but does not mean trouble free. Mine were all changed to green a couple years before I bought my car. But over the next ten years and 35k miles of driving, I replaced one or two that failed.

 

Three is the total. As I posted in PM, the right side is easy, just swap the plugs between the two to test. For the left, you will have to physically move it. Since you have two codes, for P1448 and P1445, might be better to wait until the replacements come and simply install a known good one in the bad position and test that way.

 

What's your cold idle speed at start? Could be a dirty idle control valve. You can remove it and flush it out with some aerosol carb cleaner

 

Perhaps it's simply that you're driving the car more and exposing some of the car's latent faults. Some of us were originally working on the theory that the O2 heater system was causing your cat temperature problem (i.e. because of wrong O2 readings, the ECU was perhaps commanding more fuel than was necessary). However, now that you've told us that your SD light comes on on start up, it seems you have two or more separate issues.

I'm surprised that you (and your mechanic) jumped right into purchasing new SDECUs. Did your mechanic test the thermocouple on the faulty side? You can use your multimeter to compare the resistances of the thermocouples on the left and right side. FWIW, Technistrada make some very cheap thermocouples.

Hopefully the stumbling is related to one of your other issues. Solid SD lights can shut down a bank, so that won't help. Neither will incorrect O2 readings due to heater problems.

Hopefully your tech is using his years of experience and the information you are giving him to diagnose the problem and not just "shotgunning" (i.e. throwing numerous expensive parts at the problem until something fixes it.) Any amateur can do that (with free labour).

 

If that's actually what he told you he isn't much of a master mechanic, or at least not one with 355 experience. A failed cat ECU will not cause the bypass to not operate correctly.

 

Just pull the small plug off your green-potted SDECU (the plug with the metal braid/shielded wire attached to it) and check the resistance between the two pins. Ratarossa has a video on SLOW DOWN issues, but he probably goes too deeply into things for you.



A resistance check is not ultra reliable unless you do a check across a wide range of temperatures, but at least you can check the room temperature value without burning yourself (The ones on the right hand side are hard to get to and the exhaust is nearby).

I checked the value on one of mine at 60F and got 2.2 ohms subtracting 0.3 for my multimeter leads. I had to find some spare pins to insert into the plug sockets (because my multimeter probes were too big)