Jank315

Having some issues with my 95 z28. Just picked the car up about a month ago and trying to get it running right. I have SES light on and it is setting code 43 causing the fans to stay on. I traced the wire down to the sensor and found that it did not have a sensor installed and the PCM ground that comes out with it that is supposed to be connected to the block above the starter was unhooked.i have the PCM ground hooked up temporarily to the bat ground until I can get under and fix it. I pulled the KS wire up where I could get to it and check voltage I have 4.5v with it unhooked and 2.5 with it connected. KS is at 3300 ohms to ground when tested. Im at a loss I thought for sure that would fix it seeing how it didn’t have a sensor at all. As soon as I clear the code it pops right back up. Am I missing something here or where should I check next? I don’t have the sensor in the block but it is grounded good and have it set up top where I can test it. I was trying to test it before I got under the car and pulled the plug out of the block. Also the connector for the sensor is missing so I had to make a makeshift end but it is all connected 100%.

Injuneer

How did you ground the uninstalled sensor to the block?

Jank315

I have the bottom of the sensor wrapped with wire and then grounded the wire to the ground terminal on the strut tower. Checking continuity I have ground to the engine block from the sensor. That was my first thought that it didn't have a good enough ground.
It has a MALF43c flag which I think is open circuit correct? Which I would think the PCM would still be seeing 5v on the sensor wire but when connected it drops to 2.5v.

Injuneer

MALF43a/c/d are a mystery. I've looked at hundreds of Scan9495 logs for people, and never found one of those set.

I'd still suspect that ground. Was that in place when you got the 2.5 volts between the sensor wire and the block?

The 95 factory manual indicates the code can also be set by a problem with the knock module in the PCM, faulty PCM, or high voltage interference with the signal wire. If you've got the thing rigged near a plug wire, might explain it.

Not sure why they point to the knock module. If it's missing, it would set DTC 47. Have you checked to make sure the module is in the compartment on top of the PCM, and is plugged in tight?

Jank315

Will check on the module now along with double checking the grounds and making sure the sensor wire is 100% back to the PCM. Thanks for the replies.

Jank315

At this point I’m leaning towards PCM. I pulled PCM checked module it was in place and tight. Re-checked grounds and the sensor is grounded good. I get 2.44 volts with the sensor hooked up form the sensor body engine block and battery ground. I pulled the module and got code 47. Reinstalled module checked the sensor wire right at the back of the PCM and it is getting 2.44v which should be in range and should not be kicking the code. Not really sure there is anything other to test.

GaryDoug

MALF43c isn't part of the DTC report section. It is in the engine data scan section and is apparently a refinement of the DTC43 code, since the DTC43 doesn't give a specific failure mode. This is the first time I also have seen it set since I was writing the program and forced them to be set (MALF43c when I opened the circuit and MALF43d when I shorted it). MALF43c is telling you there is no continuity to the sensor or to it's ground or that the sensor is too high a resistance value. By the way, I have no idea what MALF43a does and there is no MALF43b.

For what it is worth, on my benchtop pcm setup, DTC43 and MALF43c both set when the voltage at the knock sensor rises to 4.2 volts DC. 5.0 volts would be the maximum and would indicate a completely open circuit.

Jank315

Mine stays at Malf43c with the circuit closed, open or shorted.

GaryDoug

If that is the case even after resetting the codes, then I suspect the knock module in the pcm to be defective.

Jank315

Ok now I’m getting frustrated. I got a different pcm and started by just swapping knock module. Got the same codes and malf43c. Swapped out the PCM and same exact thing. Don’t really know where to go from here.

Jank315

I can have the key in the run position and clear codes without starting car or doing anything about 10 seconds go by and malf43c pops up.

Jank315

I also tried not using the KS and have a 3.9ohm resistor on the sensor wire going straight to ground. At D22 with the resistor hooked up I have 2.41v.

shoebox

Might be worth a try putting that PCM ground that is supposed to go to the block actually on the block where it goes. Maybe there is some ground differential between the block and the chassis. Otherwise, perhaps there is something going on with the KS lead, itself.

GaryDoug

The pcm ground is also present on it's metal case. Measure the voltage between the pcm case and the engine.

Jank315

Same voltage everywhere I ground it too. Block, terminal on fender, battery, pcm case. I thought maybe as the car was starting that the sensor wire might be seeing a higher voltage at some point causing the DTC. I have a small knick in the sensor wire right as it goes into the pcm that I made for testing. It is has 2.4 volts steady the whole time and still kicks the code. I would think it would have to be a wiring problem after swapping the pcm and knock module but I’m also I leaning towards the possibility that my old pcm fried the old knock module and when I installed this other module it fried that one too. I think that’s a long shot though. The PCM ground that was in the same harness wasn’t hooked up when I found it but had good continuity to ground so I’m assuming it’s tied to another ground. I tried hooking it back up the block as well with the same results. I thought about cutting the KS lead at the back of the pcm and running a new wire along with the pcm ground just to make sure but I really don’t want to make any unnecessary splices. I’m pretty good with wiring and am a master electrician by trade but I’m getting stumped. Everytime I think I he it I’m wrong. lol