I've been fighting the Code 43 blues for a couple of weeks now, and I'm at my wits end. To remind you, code 43 indicates a knock sensor problem. When the SES light is on, acceleration at RPM over 4500 is rough. Gas mileage has gone south, down about 25-35% from normal (22 mpg). This all is indicative of the ECM running open loop.

So, I cleaned the contacts to the sensors - no good. Saturday, I replaced the sensors (and the coolant), to no avail. I made sure to torque the new sensors to 14 ft-lbs. I'm getting the correct 5 VDC at the ends of the wires to the sensors, so now I'm getting resigned to purchasing another ECU.

I ordered a new ECM from Mid-America for $100 plus core charge. It'll arrive tomorrow. Before I put it in, I'm going to try a couple of other things to rule out wiring problems.

First, I'll disconnect both knock sensors and replace them (one at a time) with a 3.9K resistor to ground. I'll put the resistor at the terminal end of each sensor plug to test continuity of the wiring harness, then I'll put it at the ecm itself, to make sure that the ecm works OK. If the resistor works at the ecm and not at the sensor end of the wires, the problem is in the wiring harness somewhere. If that's the case, I can return the new ecm unopened for a refund.

Next, if this doesn't fix the problem, then the problem is in the ecm itself. GM suggests making sure that the mem-cal unit is properly seated - that has been the problem with some cars. So, I'll open up the old ecm and re-seat the PROM and mem-cal units.

Finally, if all else fails, I'll swap out the ecm. It's a $100 experiment, but after I've done everything I mentioned above, it is time to swap it out. I'll keep you posted.

Any more tips?



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92 LT1 Corvette, red/red, 99-44/100% stock

 

Well, nobody replied, but that's OK. I did go through the whole series of experiments last night, and it WAS the ecm. The telling experiment was cutting the wire that leads to the knock sensors and replacing it with a 1.95k ohm resistor to ground. Voltage across the resistor was a steady 1.5 volts, just like when connected to the knock sensors. Still, after resetting the ecm I got a SES light. I changed the ecm, and all is fixed. YAYYYY!