Nipper1714

Hi everyone. I have a 95 pickup 3.0 5 speed manual and got the dreaded 52 code. I did a lot of research from other threads and found it to be the corroded wire between pigtail and knock sensor. I bought the OEM wire from Toyota dealership and began the tear down. What really sucked it when i got down to the knock sensor to pull off the connector, the plastic female end on the knock sensor broke. So i had to buy a new knock sensor. I got one from O'Reilly's and put everything back together. I still get the 52 code but its intermittent, meaning it will only throw the code if I'm under 65mph. I did more research and saw that all aftermarket knock sensors are junk and that I should have gotten the OEM one from Toyota. Does anyone think this is the problem? Timing btw is is set to fsm spec.

Kiroshu

Welcome to YotaTech!

It would have been my suggestion to acquire a factory replacement Knock Sensor as well.

Make sure your knock sensor wiring harness connections are clean and tight.

Verify no damage to wiring harness. Breaks/damage/frayed wiring.

Code 52 is very specific and is either the knock sensor/knock sensor wire/ECM fault.

Any engine performance issues..?

Poor quality fuel..?
Fuel contamination..?
Ignition system faults..?
Engine timing correct..?

Nipper1714

There are no engine performance issues. Heck, when the cel doesn't kick on it runs absolutely great. The fuel i run is 93 octane because i was thinking i had and engine knock. I doubt it any ignition issues but I could be wrong. Changed plugs and wires 3 times since I've owned truck and plugs looked fine. Timing is set to TDC which if I'm not mistaken is 10 degrees...haven't looked at the fsm in a while, but I know its set.

Thought it might have been the pigtails and checked continuity through pigtail and that checked out. Its weird because WHEN the code is thrown is also affected by temperature. During the summer when its 85+ the cel will come on b4 i can make it 2 blocks down the road. When its below 70 i can drive under 65 mph and it won't come on until the engine gets up to operating temp.

If code 52 is specific to wiring, meaning the ecm either DOES detect the knock sensor or it DOESNT detect it, the why would temp or what speed Im at affect if the code is thrown? It doesn't seem like it to me thats it's the wiring. When it comes to electric and wires, it either works or it doesn't.

Ugh.

Kiroshu

Haven't seen the wiring diagram in a long time but I believe the knock sensor on the 3VZ-E as are many Toyotas is a one wire system that goes from the knock sensor straight to the ECM.

The knock sensor serves as a ground to the engine cylinder block and is a variable resistance sensor.

Knock sensors are very sensitive to damage. If it was dropped or hit it may have already been damaged prior to install.

Knock sensors should always be Tourqed to specifications. Over or under tourqing the sensor may also have caused damage.

Its very rare that a ECM fault occurred but it is possible. I would start with replacing the knock sensor with OEM Toyota and be very care full.

shaeff

None of the above would cause a code 52.

scope103

No. A knock sensor is a piezo device (like an old-fashioned "crystal" phono pickup) that produces an AC signal. It's resonant to a certain frequency typical of knocking, but it is a small signal that must be amplified by the ECU. Because the signal is so small, the knock sensor wire is shielded to reduce engine EMI.

If it was a resistance sensor, you could test it with an ohmmeter. No such luck.

Actually, knock sensors are very tough. Think of the environment (right on top of the block) that they live in all day. Of course, they aren't bullet-proof; if you clobber it hard enough it will break. But in most code 52's, it's the wiring, not the sensor.

I wish. If you have a hole (crack/split/etc) in the shield somewhere, vibration and moisture (and to a lesser extent, heat) will affect how well the shield works, and if it doesn't work well enough the ECU will not be able to pick the knock sensor signal out of the background noise.

As you've figured out, code 52 has nothing to do with whether the engine is knocking, so octane, plugs, timing, all make no difference.

RJR

Edit: I wrote this in parallel with scope103, thus some duplicated info.

As has oft been stated here, code 52 means the ECU can't detect a signal from the knock sensor. Has nothing to do with whether or not the engine is knocking - thus shaeff's correct statement about the things that won't cause a code 52.

While drawn as a resistor on the wiring diagram, the knock sensor is actually a piezoelectric microphone, with a resonant peak around 7Khz, the characteristic knock frequency. Piezo's put out a fair amount of voltage (a few hundred millivolts), but they are very high impedance, which makes the wiring susceptible to induced electric field (voltage in adjacent wiring) noise. When you consider the engine comparment also contains unshielded ignition wires sparking at 25,000 volts, you can appreciate the need for good shielding on the knock sensor wiring.

The signal lead of the knock sensor goes directly to the ECU sense circuitry. The ground return path is furnished from ECU-frame-engine block-knock sensor. A braided shield, grounded at the ECU end only, provides electric field shielding for the signal lead. It's important that the shield not be grounded anywhere else as it passes through the engine compartment and cabin, otherwise ground loop currents will induce noise into the signal lead.

Get all these wiring details correct, and a good knock sensor, and your code 52 should go away.

Edit#2. It would be nice if electronic circuits either worked or did not, but as scope says, that's a dream world. Intermittent operation due to temperature change or mechanical vibration cause no end of grief for troubleshooters.

Kiroshu

I really don't know why I stated that "the knock sensor was a variable resistance sensor."

I knew about the internals of the sensor and the vibrating/crystal generating a signal for the ECM and I still typed that in.

Kind of embarrassing really..

Very awesome clarification as stated above.

I apologize to the OP.

I love to learn.

"And now we know, and knowing is half the battle." GiJoe!

I never said the list of symptoms described causes code 52 they more or less points of interest for the OP in case of other problems that may or may not be present. I was more of less triggered to say it when he mentioned he "set timing to FSM" indicating he may or may not be trying to remedy a performance issue.

Also I only spoke of the knock sensor fragility based on experience. And it was one of the things my mind stuck glue to when I was in college for auto repair. My instructors always told me to be careful with knock Senors that the crystal inside of them is too easily damaged. Take Care and tourqe to spec they said.

Thanks this has been interesting.

scope103

Kiroshu -

Sometimes people dig these threads up years later, so it's a good thing that someone will jump in and clarify a point made a little too broadly. I've made mistakes in posts, and I try to go back and edit out the mistake (or delete the post entirely), even if the discussion has long since moved on.

So we aren't picking on you (and you won't be picking on me when you do it). We're all just chipping in to keep the information as clear as we can.

Kiroshu

^--- Thanks