Frustrated - Reversing Sensors

[kenjosh]

I am getting very frustrated as I seem to have got to a dead end. The other day I picked up a 60cm stick sticking out of the curb (yes I live in the country) and it gave the rear wheel arch a heck of a whack. I stopped and had to remove it as it was jammed in the wheel arch. No damage was apparently done to the car, none visible anyway.

However, the following morning, reversing the car out of the garage, the reversing sensors just gave a loud constant rhythmic tone. The sensors were fitted 2 years ago by Mr T - a special offer.

I trawled the forum for previous advice. Then removed the various bits of fittings at the back of the Avensis Estate (58 model) and got access to the ECU and wiring. I removed each sensor in turn and then all of them. It had no affect on the sound. So I thought - must be the ECU as it is velcroed onto the wheel arch and must have been damaged in the bang.

Searched for a used version of the ECU but no luck. Tried Mr T who was able to get a new unit (a Cobra one made for Toyota) for £59 plus Vat. Got it today and put it in expecting everything to be OK. However, no change!!. Have checked all the wiring to the sensors. Everything checks out OK.

Anyone got any ideas what I have missed. There are only 2 things surely that could be at fault, sensors or ECU. Be grateful for any advice or suggestions.

[dew66]

Ken,

According to another online forum, the Cobra system need to be calibrated as described here:

Some parking sensor kits (like marketed by Cobra) require calibration before use; there are four simple steps.

(1)

Park your car 50cm from a convenient wall.

(2)

With reverse selected, turn ignition on until unit sounds constant tone for approximately two minutes.

(3)

Turn the ignition off and cut the blue looped wire exiting the control box.

(4)

Insulate the cut wire ends. If a sensor has to be replaced this wire will need to be reconnected and the above procedure repeated.

Don't know if that is relevant but might be worth investigating.

Dave

[kenjosh]

Hi Dave

Thanks for info. Unfortunately I have no blue wire. Only the 4 sensor wires, speaker wires and the power connector which links in to the reversing light circuit so the ecu becomes active when the gear stick is put into reverse. No other connector on the ecu box. Never thought about callibrating it though. Perhaps I will have to give Mr T a ring.

Ken

[dew66]

Ken,

Another possibility is that the speaker is itself a sounder - emitting a tone sound when it receives 12 volts - in which case it could be the case that one of its wires, which would normally be pulse connected to the 0v by a pulsing output signal from the ECU, has somehow got itself a continuous short circuit connection to 0v .

However I'll agree with you - follow through the calibration aspect as the next line of enquiry, with Mr T.

Dave

[kenjosh]

Hi Dave,

Had a chat with local Mr T this morning and they said that the ecu is plug-and-play and does not need calibrating. They said to try and feel each sensor vibrating with your finger gently on the surface of the sensor when it is in reverse gear with engine off and ignition on. The one that does not vibrate is the faulty one. Did that but cannot feel any vibration from any of them - perhaps my fingers are not very sensitive. Anyway with all the sensors out of the ecu, it makes no difference. Checked the speaker wiring and seems OK. No visible shorting.

Avensis due for service in 10 days. Might have to let Mr T look at it for me then.

Ken

[dew66]

Thanks for the info Ken.

I'm not fully convinced that there is no calibration for the Cobra sourced ECU, but Mr T should know best.

Would be interested to hear the outcome of this.

[dew66]

Ken,

A later thought - still on the theme of calibration - there may not be any visible blue wire, but are there any unused pins in the power connector, or elsewhere on the unit?

If so, these could be associated with a "manufacturing / dealer only" procedure which sets the thing into calibration mode.

Dave

[kenjosh]

Dave,

Checked the new ecu which I have kept aside at the moment, and no spare connections so I think it must be as they said, plug-and-play. Had a look at similar Cobra units and there is no mention of calibration with them either.

Will keep you informed of developments.

Ken

[gazza1286]

Have you checked to confirm that power is reaching the module when reverse is engaged?

[kenjosh]

Dave,

Had a productive weekend and identified the fault. Number 2 sensor - not the ecu which we now knew anyway.

Found a great guy on eBay (Ice4cars) selling Cobra parts and giving advice. He said that rarely will an ecu go, and even if they did, a new one is about £30 (Mr T's was nearly £70 - and unfortunately will not take it back because it was a special order.)

To diagnose fault, unplug the speaker from the ecu, put car into reverse gear with ignition on and then put your ear to each sensor. You will hear it vibrating - which you can. The one that does not vibrate is faulty. To check it is not the wiring, swop over the wire on the ecu connected to the "faulty" sensor with one that works. Check the sound again. Should still find the sensor not working if wiring OK. Have ordered a new replacement sensor from him (about £17 including recorded delivery). When it arrives will use touch-up paint (£8 from Mr T) to colour match. (Sensor comes with protective ring to prevent paint getting onto vibrating membrane).

I expect some fun getting old sensor off but there is no-gain-without-pain, so they say. The sensors by the way are numbered from the passenger side out to the driver side.

Ken

[dew66]

Thanks for update Ken. I take it that the correct operation of the parking sensor system will not be possible until all sensors are installed and all working - so you still don't know about the plug and play aspect? BTW I found an online manual for some Cobra systems that don't have the blue wire but do have a programmable capability for several functions including volume level and different sensitivity settings for inner and outer sensors

[kenjosh]

Hi Dave,

I can now bring this sorry saga to an end. Got underneath the car yesterday and managed to first get the rubber dust cap off the rear of the sensor (which I thought was No. 2), and the wire spade connector easily came off with it - which made me a bit suspicious. Pushed out the old sensor and put the new sensor onto the end of the wire to check all was OK before putting it back - and it was. Double checked by putting old sensor back on - and it too was OK!!! I think the spade connector had come loose and was giving me the fault and because I thought it was sensor 2 (not sensor 3), swopping wires 1 and 2 on the ecu made no difference. What I should have done was to try 3 and 4 and then I would have found it was a cable not the sensor. Does that make sense?

So all in all, what have I learned from this escapade? Well : -

1 - a reversing sensor ecu is unlikely to break, even if it is attached to the wheel arch and unless the fault is corrected it will always give the constant noise.

2 - use your ear to check each sensor once the speaker cable is removed from the ecu

3 - double check the wiring from the ecu to the sensors and do not assume that No. 1 sensor is the passenger side and 4 the driver side.

4 - replacing an ecu from Mr T will cost more that buying a whole new cobra kit from eBay.

Hope some of this info helps others in a similar position. Thanks for the moral support and suggestions Dave.

Ken

[dew66]

Ken,

Thanks for the final report- good information which could be helpful to many others. Glad you reached a satisfactory outcome.

Dave