Some of this would apply to the later 1MZ-FE V6 also.
Retrieving the error codes:
To read the error codes, follow the instructions on this website
. For the '92-'93 V6 Camry which has OBD I, the error codes related to knock sensors are listed below.
52 = Knock Sensor signal, left bank (front, nearest radiator). No number 2 knock sensor signal to ECM for 2 crank revolutions with engine speed between 1,600 and 5,200 RPM.
53 = Knock control signal. Engine control computer (for knock control) malfunction at engine speed between 650 & 5,200 RPM.
55 = Knock Sensor signal, right bank (rear, near the firewall). No number 1 knock sensor signal to ECM for 2 crank revolutions with engine speed between 1,600 and 5,200 RPM.
Diagnosing the source of the error code:
53 is caused by a fault in the ECU per the FSM. I'd interpret that to mean the ECU is bad; replace it.
52 & 55 can be caused by faults in the ECU, the wiring, or the sensors. So it's best to try to narrow it down. The ECU cannot be checked, so the only thing that can be done is to check sensors and wiring. If they check out OK, then replace the ECU.
FYI: Toyota uses "resonance piezo" knock sensors that put out a 7.6 kHz signal at all times, whether the engine's knocking or not. The ECU is constantly looking for this 7.6 kHz signal when RPM is between 1,600 & 5,200, and if it doesn't see it, it throws an error code. Once the code is thrown, ignition timing is retarded (to zero degrees BTDC, near as I can figure out), which cuts HP pretty badly. Here's a youtube video that talks about Toyota's resonance piezo knock sensors:
Checking the knock sensors:
There are two tests that can be performed. One is to check resistance, the other is to check the live signal with the engine running using an oscilloscope.
The sensors are located under the intake manifold, which makes them inaccessible without tearing it apart. Fortunately there is a short cable that runs from them out to the front right side of the engine where it connects to the main wiring harness. The pic below shows where this connector is. Unplug it to check resistance at this point in the wiring.
Here's a couple pics showing how to find that connector on the 1MZ-FE. It's not nearly as convenient. This first pic shows the cable where it exits from under the intake manifold. I've marked it with a red line.
Follow that cable to the connector, boxed in red in the pic below. Roughly, it's under the throttle body.
In the picture below, the knock sensor signal wires are at pin 1 (rear sensor) and pin 2 (front sensor); the other two terminals serve to connect the cable's shielding to ground. Measure resistance from pin 1 to a good ground and pin 2 to ground. I stress *good* ground. I first checked using the front exhaust shield as a ground, and was getting screwy readings. When I checked resistance from that shield to the battery negative terminal, it was nowhere near zero. It *must* be zero; this is important! So I measured to the battery neg terminal to avoid getting a bad reading. The resistance from the sensor's signal wire to ground must be greater than 1 megohm (1,000,000 ohms). If the resistance checks below 1 megohm on either sensor, it's fairly safe to conclude the problem is not the ECU, but it could be the knock sensor or the short cable going to them. If the resistance is infinity (open circuit), there's a good chance the cable is broken or disconnected from the sensor; the FSM does not say this, that's my opinion. On mine, the rear sensor measured 0.300 megohms; bad!
Checking sensor output with an oscilloscope:
Turn on your o-scope and set the time scale to 100 microseconds/division, and the voltage scale to 200 mV/division. With the connector described above unplugged, start the engine. Connect the scope's signal probe to one contact and the probe's ground lead to a good ground. The engine needs to be revved a bit for the sensor to generate a measureable signal; roughly 2k RPM. The FSM says 4k RPM, which I found unnecessary. At idle, they'll put out just a small ripple. A good sensor will put out a signal as shown below. The rear sensor on mine was flat-lined. So I've either got a bad sensor, or the short cable is bad. Either way, the intake tract needs to be taken apart to inspect and replace things.
If you find nothing wrong in either of these checks, either the main wiring harness is bad, or the ECU is bad. To check the main wiring harness, check resistance in the cable connected to the ECU from pin 6 (signal KNK1) to ground, and pin 14 (signal KNK2) to ground. The glove box must be removed to access the ECU. Again, resistance should be greater than 1 megohm. If it checks OK, chances are the ECU is bad. If it checks bad, there's a problem with the main wiring harness... and I have pity on your soul. Good luck finding that problem!
Replacing the sensors & cable:
If you've determined there's a problem with one of the sensors or the short cable going to them, it's time to take it apart and replace things. I decided before starting that I was going to replace both knock sensors and the short cable. This is a big enough job I didn't want to risk having to do it again soon. I ordered the cable and two sensors for ~$300 from ToyoPartsman
, Gary Smith at Newnan Toyota. I also ordered a Fel-Pro gasket set for $40 from Rockauto. And a tube of silicone sealant locally for resealing the coolant bypass tube, a "while you're in there" job I highly recommend doing. You'll also need coolant to refill the cooling system when you're done.
Fel-Pro gasket set = MS95406
Knock sensor = 89615-32030 (this p/n replaces 89615-33020)
Short cable = 82219-33010
First, drain the coolant by opening the petcock at the bottom of the radiator on the engine side. It's circled in the pic below. This is necessary because there are coolant passages in the intake manifold. If it's not drained, when the intake manifold is removed coolant will spill everywhere and make a big mess. Worse, some could drain into a cylinder with open valves and hydrolock it. Don't be foolish, drain it. Google "hydrolocked engine" pics if you feel a need to see bent and busted connecting rods.
Use an allen wrench to remove the two fasteners holding the decorative intake cover (no pic). As shown in the pic below remove the 4 bolts circled in red, unplug the injectors circled in yellow, and disconnect the vacuum lines in green. Set this assembly aside to the right.
Remove the big flexible rubber intake duct running from the MAF sensor to the intake mouth.
Remove the intake plenum 2 bolts and 2 nuts circled in red below. When reassembling, torque these to 32 ft-lb.
Remove the 4 hex huts (reassembly torque 9 ft-lb) holding the ACIS actuator to the plenum. Disconnect the banjo bolt (reassembly torque 11 ft-lb) fuel connection to the cold start injector, and the vacuum line going to the vacuum motor. Set it aside as shown and remove the gasket. Also disconnect the rubber hose going from the PCV valve to the nipple on the underside of the intake plenum. Use the new gasket from the Fel-Pro set on reassembly.
There are 5 fasteners on the backside of the plenum that must be removed. One on the left...
And two in the middle (reassembly torque 13 ft-lb), which bolt the EGR pipe to the back of the plenum (see pic later). Mark with a Sharpie, and remove these vacuum lines...
Unplug the ECT sensor (green plug) and the cold start injector timer behind it, both on the left in this pic. On the right, disconnect the throttle position sensor connector, and the IACV connector (blocked from view, it's underneath the rear cylinder circled in blue in this pic)...
Now lift the plenum, and disconnect the three coolant lines underneath shown below. You now should be able to move the plenum to the driver's side of the bay, out of your way (unless I've forgotten something, which is possible, so check). Also, see the EGR pipe I said I would mention earlier?... in the lower left of this pic.
With the plenum removed, STUFF SOME RAGS INTO THE INTAKE MANIFOLD PORTS TO KEEP FROM DROPPING THINGS IN THERE!!! Yes, I meant to yell. It would really suck to drop a washer through an open valve down into a cylinder, and have to remove the head. Then remove the two bolts circled in red and disconnect the three injector connectors circled in yellow, and set the rear injector harness aside to the left...
Disconnect the upper radiator hose and the small coolant hose going from the thermostat housing to the coolant reservoir (no pic). Remove the 8 bolts and 4 hex nuts (reassembly torque 13 ft-lb, work from middle outward, doing it in several passes). Warning: The bolts have two washers each, and the nuts have a captive washer and a loose washer; don't drop them. The short bolts (yellow circles) go in the outer holes, and the long bolts (red circles) in the inner holes. Also remove the bolt holding the ground wire, and a metal bracket. These two are out of view, on the left, next to the thermostat housing). There is one electrical connection (in blue) to undo to the intake manifold. Sorry for not getting everything in this pic, but I had my camera bumped into the hood looking straight down, and this is as good a pic as I could get. Note that you're seeing some things in this pic that shouldn't be there... that's because I forgot to take this pic until I was putting it back together.
Now lift up on the manifold, revealing the knock sensors (in big red circles below). Unsnap the knock sensor cable anchor circled in yellow. Remove the hex nut in the small red circle; this will allow the coolant bypass tube to be lifted out of place.
Remove the two bolts holding the coolant bypass metal tube flange and lift it out. At this point, you can re-check knock sensor resistance to verify which sensor is bad. Before reinstalling the bypass, remove and replace the knock sensors, torquing to 33 ft-lbs. Install the new cable, snapping it into place, and routing it out to the main harness. Reinstall the small hex nut holding that end-plate.
Thoroughly clean the bypass tube flange and the mating surface in the block. Apply sealant to the bypass flange as shown, insert into the block, and replace the fasteners, torquing to 6 ft-lbs.
Remove the old intake gaskets and clean both mating surfaces thoroughly. I also scraped out the carbon in the mouths of the intake ports in the heads. When done, I used a shop vac with a small flexible nozzle to suck out any carbon debris that may have fallen into those ports.
Reassemble in reverse. Take your time, double check that everything gets hooked back up correctly. Don't pinch anything under the intake manifold! (*%$*&!!!... I can be such a dope sometimes!) Take lots of your own pics before disconnecting things; that can really save you from getting stuff wrong.
After reassembly, remove the radiator cap at the thermostat housing and refill the system with coolant. Check for leaks, especially at the intake manifold's coolant galleys on each end. With the cap still off, start the engine and top off as needed. Keep watching and topping off until the engine is fully warmed up. And continue to keep an eye out for leaks. You'll see the coolant level drop many times, with an occasional bubble burping out. Keep adding coolant as needed until it won't take any more. This is important, so don't be in a rush! The 3VZ is fussy about air bubbles in the cooling system, and will overheat if you don't get this done properly. Even after doing this, it's a good idea to closely monitor the coolant level in the overflow reservoir for a few days, topping off as needed. I've had to top it off twice in the week since I've finished the job. And the CE light has remained OFF!
Oh, and here's why you should buy the cable, even if it's not the source of the problem. When I went to disconnect them, the connectors at the knock sensors crumbled like egg shells at the first touch.