How To Test A Bosch Dishwasher Control Board

[Algernon Alcala]

BoschSHS5AV55UC/22 Dishwasher.

I'm a relatively intelligent and intuitive person, and a teacher, so also very patient. But this one has me stumped. I've got a multimeter and testing cords, and have checked every component to the best of my ability, and replaced parts in an attempt to troubleshoot. Each individual component seems to work fine outside the machine when bench testing, and switches send signals as they are supposed to. Here's what I have done / think I know so far:

Problem: water inlet valve does not activate > replaced, bench tested OK > does not activate with drain pump 3 > drain pump 3 works outside machine when attached to control board AND inlet valve activates (puzzled)

Problem: drain pump installed (working for first part of cycle > manually activate water inlet valve when signal sent from control board (machine fills, circulation pump runs, drain pump cycles) (puzzled)

Problem: not draining: WORKING water inlet valve installed, WORKING drain pump installed, Control Board 3 (working?) installed > GoPro and a light inside the machine: run Auto cycle > runs program as follows:

No worries, my tail then. Had a Electrolux dishwasher with intermittent drain, replace drain pump twice, snaked the drain tube everytime. Still intermittent draining, gave up and ordered drain tube due to the builtin check valve. Replaced the hose then asked the customer if could cut open the old drain hose, she said sure. Found a clear plastic foot from a counter trivet stuck in the check valve. The snake would just past thought without any issues. Impossible to see due to color and a snake would just flip it sideway and pass through. If you problem persists maybe worth a look as your check valve is separate from the drain hose.

Listened to the video the drain pump is ticking like it is trying to start. Since it runs with no load we come back to control issues. Remove the cover item 0434 in my picture, check for burrs in the cover and sump. When reinstall the cover make sure it is tight. Which error code are you getting 24 or 25? If the drain pump cover is good you can try a reset.

I have a Bosch SHX57C05UC dishwasher. While it was running today, it made a kind of hammering noise and then started overflowing. I was out, but my wife turned off the water and left it until I got home.

One more detail. When I was testing that the door switch is working, I noticed something that might be odd. Testing voltage from N on the power switch to the closed post of the door switch, I get 120V, which is expected. Measuring to the open post of the door switch, I got 110V, which seems odd to me, but I guess could be normal? (Tripping the switch causes the posts to swap, as expected.)

New behavior to report! I noticed that if I close the door hard, the washer begins draining, but it only lasts for about 1 second, then it shuts off again. Closing the door gently (less than hard) has no effect. I struggle to see how that can be anything other than a bad door switch. BUT, when I took the switch out, I could see with a meter that resistance across the closed posts was 0, across the open posts was infinite, and they swapped when I triggered the switch. Could it be that the switch is failing in some way that affects the current/voltage, but not the resistance?

I pulled out the washer this afternoon, took it completely apart, cleaned everything out, and put it back together. I found a build-up of gunk on the filter inside the water inlet valve. It looked like enough to be blocking water flow. I also checked out the turbidity sensor, and it passed visual inspection.

After I put everything back together, I powered it up (outside with no water attached), and noted no difference in behavior. The washer doesn't seem to recognize that the door is closed. While I had it lying on its back I noticed again that if I closed the door hard enough, the drain pump would run for about a second and shut off again. After I stood it upright again, it went back to completely ignoring the door, regardless of how hard I closed it.

I finally got some time to dig a little deeper. First I built shunt to replace the switch, so that the washer always thinks the door is closed. With the shunt in place, it still acts like the door is open. The switch is officially exonerated.

As before, I was able to manually trigger the float switch to get the washer to drain the water. That is the only way to make the washer drain. Activating the drain function from the controls has no impact.

The flood switch is tripped. This is located under the unit. Unplug or flip the breaker to the dishwasher, take off the black kick plate under the door, 2 screws, and you will see the white plastic "pan". The flood switch is located where you can't really see it but it is on the left hand side wall and is made of styrofoam. The best thing to do is to put some rags in the pan, this is not easy because there is little room to put them, and soak-up the water that has filled the pan. Eventually you will get enough water out that the float will deactivate the switch. What you hear "running" when you turn it on is actually the drain pump, it get activated when the flood switch is tripped.

a) The washer never acknowledges that the door is closed. I have checked with a meter that the door switch is operating correctly; the signal that the door is closed is definitely getting to the control board.

Bosch dishwasher e6 error code. An E6 error code of the Bosch dishwasher means that there are problems with the sensor that controls the water turbidity. ... In the dishwasher, this sensor detects the turbidity of the water due to the presence of small particles of dirt, food residues and other things inside it.

I pulled out the washer this afternoon, took it completely apart, cleaned everything out, and put it back together. I found, just like you described, a build-up of gunk on the filter inside the water inlet valve. It looked like enough to be blocking water flow. I also checked out the turbidity sensor, and it passed visual inspection.

After I put everything together, I powered it up (outside with no water attached), and noted no difference in behavior. The washer doesn't seem to recognize that the door is closed. While I had it lying on its back I noticed again that if I closed the door hard enough, the drain pump would run for about a second and shut off again. After I stood it upright again, it went back to completely ignoring the door, regardless of how hard I closed it.

I can believe that the crud I cleaned off the valve filter was the cause of the howling. It doesn't explain the original overflowing, though. Nor does it explain the washer acting like the door is always open.

I just reread your post, and I don't think the first line sank in the first time. So, you're saying that if the washer thinks the turbidity sensor is bad, then it won't turn on regardless of what the door switch is or isn't doing? Shouldn't the washer give some more obvious signal than just refusing to start? Aside from the part where it won't start, the UI is behaving perfectly normally, which seems very misleading. Why give me the option to select a cycle or cancel-drain if the washer has no intention of running it?

I'm full of questions (or something) because parts for this model are stupid expensive, and I'm trying to avoid dumping hundreds of dollars into parts just to find out there's a control board failure. I also like the switch as a scape goat because it's the cheapest thing I can replace. :). Thanks for bearing with me.

A few weeks ago I looked at a Bosch DW for a friend, that one was completely dead and had an obvious blown up chip on the main board, the board was $388 so the machine was replaced with a new F&P dishwasher. I have the dead one in my shed.

Now another friend has asked me to look at their Bosch dishwasher, a similar model but a few less features. Both approx 10 years old. The second one is a Bosch SMU50E15AU. I assume the AU on the end just means Australian market. This one tries to work, it does an initial pump out, then at fill stage it doesn't fill. It is NOT the fill solenoid, I have checked that and it is OK. I believe it is a main board fault again. This board is $420 but I have the other machine's board to pinch components from, it is almost identical but not quite. I'd like to try to get this one working by swapping components from the other board, but I can't find any obviously faulty components. It is mostly SMD devices so this will test my soldering ability.

First up, I'd really like a repair manual for this SMU50E15 dishwasher, can't find one online. Does anyone have a link to a suitable manual for this model or something similar? 10 years old, Bosch, made in Germany.

So far... the solenoid is 240 V AC and there are tracks on the board for both Active and Neutral 240VAC, not through the switchmode power supply. These appear to be all OK - I can measure continuity to the switching triacs for all the solenoids, which are on the neutral side. The Active side - feed to the solenoids leaves the main board, goes to the flood float switch in the base, then back to the board, then out to the solenoid, the solenoid neutral is switched by a triac. All this circuit tests OK from AC Line in (Active) through float switch, solenoid to the triac. So it appears either the triac is faulty (not switching on) or not being switched - the microprocessor switches it through a transistor and a couple of resistors. The transistor may also be faulty, the resistors test OK. There are several identical circuits, one for each solenoid, and they all check out the same when I check the components resistance from terminal to terminal with a multimeter. So unless I'm missing something, either a transistor or triac (that physically looks OK and tests the same as its neighbours with simple resistance tests terminal to terminal) is faulty, or the microprocessor is kaput.

The other possibility is some sensor is detecting a fault and so the processsor is not commanding a fill - but that appears unlikely, as the machine sits and waits for a fill, then appears to time out and goes to "end" and displays a "check water" light. It doesn't have any useful display, just an "active" LED during operation, plus LEDs for End, Check Water and Rinse Aid.

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