cruise control ECU

[ian_s]

my cruise control stopped working a while ago, and I've finally got round to having a look at it. i ran through a load of diagnostic tests that i got from somewhere and basically narrowed it down to the ECU being faulty. so i just took the ECU out, opened it up and found what i think is a blown capacitor

am i right in thinking thats the case?

is it possible i could replace the offending component and it'll work again or is it totally knackered?

[gadget]

The capacitor at the front of those two photos isn't obviously blown.

I can't see the one (possibly two) at the top edge of the board properly (behind the copper heatsink)

[CwazyWabbit]

The white stuff is just glue to stop vibration problems.

I notice the metal washer on the connector is furry showing possible damp, what is the track side of the board like? Also the relay contacts?

[ian_s]

heres a few more pics

i cant see any other signs of damp, and no obvious dry/broken joints

[Steve 110]

Might be stating the obvious here but is the ecu being powered up (ie getting it's 12v feed)? You could potentially have a wiring fault.

[gadget]

There's nothing obviously toasted on that board.

You'd need to check the feed(s) as mentioned above, and then check the components.

Can you borrow an ecu from someone and test with that to confirm that it is the ecu that's at fault?

[tjolliffe]

Are you sure it is an electrical rather than mechanical issue? Have you checked all the lines for a vacume leak?

[ian_s]

I've got somewhere a document i printed ages ago for diagnostics, and I've run through that checking it all, but if i can find it again i'll run through it all again.

the vacuum piping is all ok, i replaced it all when i bought the car a few years ago. now if i take it off the pump and apply a vacuum you can see the bellows move the throttle arm, and it holds the vacuum for a long time. pressing the brake pedal lets air back in as expected. it's an auto, so no clutch switch to check.

the pump runs when you apply 12v to the right pins, and you can see that operate the bellows again.

anyone local to Medway that i can borrow an ECU off to check? i've had an offer of one but i wont be able to get it for a while

[ian_s]

this is basically the procedure i followed to test the wiring. it's not exactly the same but seems to cover what i did

1. Turn ignition on. Turn CC system on. Put transfer case in HI range and gearshift in forward gear. (from this point forward I will say "in drive" to mean the previous sentence). Ensure clutch pedal is released. Disconnect cruise control ECU connector. Connect negative lead of voltmeter to CC ECU harness connector terminal no. 8 (black wire) and positive lead to terminal no. 10 (orange/white wire). If battery voltage exists, go to step 3. If battery voltage does not exist, go to next step.
2. Turn ignition off. Using ohmmeter, check resistance between ECU harness connector term. no. 8 (black wire) and ground. If resistance is less than one ohm, go to next step. if resistance is not less that one ohm, repair black wire between CC ECU and ground.
3. Ensure ignition and CC system are on. Disconnect CC ECU connector. Using voltmeter, check voltage between CC ECU harness connector term. no. 4 (red/yellow wire) and ground. With RESUME/DECEL switch pressed, battery voltage should exist. With RESUME/DECEL switch released, no voltage should exist. If voltage is as specified, go to next step. If voltage is not as specified check circuit from steering wheel switch to CC ECU.
4. Ensure ignition and CC system are on. Ensure CC ECU connector is disconnected. Using voltmeter, check voltage between CC ECU harness term. no. 3 (gray/yellow wire) and ground. With SET/ACCEL switch pressed, batter voltage should exist. With SET/ACCEL switch released, no voltage should exist. If voltage is as specified, go to next step. If voltage is not as specified, check circuit from steering wheel switch to
CC ECU.
5. Ensure ignition is on. Ensure CC ECU connector is disconnected. Using voltmeter, check voltage between CC ECU harness term no. 5 (green/purple wire) and ground. With brake pedal pressed, battery voltage should exist. With brake pedal released, no voltage should exist. If voltage is as specified, go to next step. If voltage is not as specified, check green/purple wire between CC ECU and stoplight switch. Check stoplight switch. Repair as necessary.
6. Turn ignition on. Reconnect CC ECU connector. Using voltmeter, back-probe between CC ECU harness term no. 11 (yellow wire) and ground. Spin a rear tire at about 3 MPH. Voltage should be about 2.5 volts, or vary between zero and 5 volts. If voltage is as specified, go to next step. If voltage is not as specified, check yellow
wire from CC ECU to the vehicle speed sensor. Check ECU. Repair as necessary.
7. Turn ignition on. Turn CC system on. Disconnect CC ECU harness connector. Connect a fused jumper wire between CC ECU harness term No. 1 (Orange/blue wire) and battery voltage. Connect another fused jumper wire between CC ECU harness term no. 7 (orange/red wire) and ground. If vacuum pump operates, go to
next step. If vacuum pump does not operate, check orange/blue and orange/red wires between CC ECU and vacuum pump. Check Vacuum pump. Repair as necessary.
8. Ensure ignition and CC system are on. Ensure CC ECU connector is disconnected. Connect a fuse jumper wire between CC ECU harness term. no. 1 (orange/blue wire) and battery voltage. Connect another fused jumper wire between CC ECU harness term. no. 7 (orange/red wire) and ground. Connect another fused jumper wire between CC ECU harness term. no. 6 (orange/pink wire) and ground. Vacuum pump should operate, valve should close and throttle should open wide. If system operates as specified, repair CC ECU. If system does not operate as specified, check orange/pink wire between CC ECU and vacuum pump. Check vacuum pump. Repair as necessary.