Cruise Control worked for one day (now broken)

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pwood999

pwood999

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Guys,
Early this week my cruise control started working for the first time in four months. . . . but stopped working the next day :(

So I went through the Rave Diagnostic procedure again . .
  • Test-A: 12.6V at ECU pins 8-10. Pin 8= 1.1ohms to chassis.
  • Test-B: 12.6v at Inverter Module. RES line switches at Inverter and ECU
  • Test-C: SET line switches at Inverter and ECU
  • Test-D: Brake pedal switches ECU Pins 5 & 9 0v-12v ok.
  • Test-D3: Used Oscilloscope to check speed pulse. 0-5V square wave when turning front wheel, so BECM must be passing speed data (can the BECM send invalid speed data ? . . . and is the speed pulse used anywhere else ?)
  • Test-D4: Shorting pins 1-9, and grounding pin 7 operates Vac Pump ok.
  • Test-D5: Shorting pins 1-9, and grounding pins 6 & 7 operates Vac Pump, and pulls throttle wide open.
  • Skipped the remaining tests due to access to BECM.

Vacuum lines are OK, and Test-D5 shows this by maintaining vacuum as long as the pins are connected.

Lastly, I opened up the ECU and re-soldered most of the pins, although there was no signs of dry joints or corrosion.

Given that the Cruise worked on Tuesday, but now stopped again I am at a loss to figure this out.

Any Ideas greatly received ?

Thanks,
Pete
 
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Did the throttle move on the vac bag (just behind the EAS box) I know its not possible to see it when the car is stationary but you can put some tape on the cable and see if it has pulled and is the operating bag in good condition and no holes? obviously you would know if it had whilst driving. Also there are vac pipes that go into that unit that perrish and split? this is the most common problem and a silly question did you depress the cruise control switch to enable the cruise control before you can enable it?
 
Yes Vacuum Pump works, and pulls the throttle wide open on that test. It holds solid until I either press the brake or remove the wire to pins 6 & 7.

I dismantled & refurbished the pump & valve about 2 months ago, and bench tested them using 12V and croc-clip wires !!

All vacuum pipes are ok with no splits. If there were splits then the vacuum hold test would not work.

I'm fast heading toward the "replace with later ECU" modification, but having trouble locating the loom for the newer ECU.

Pete
 
Can you say what car you have Petrol Diesel and year etc.

Have you checked the electrical connectors on all the components inc the multiplug from the bottom of the vacuum control unit, the brake and clutch pedalswitches.vent and the inverter/converter multiplug. And ECU plus the connector to the BeCM. Also make sure you don't have a sticking steering wheel switch/s set/+. Is the switch on the centre switch pack working? Lots of connectors!
Should work after 30 mph and disengages over 125mph or 5000 revs (especialy on the way to work!)

ps C255 (up to 99my) C1279 (from 99my) 20 pin white connector on the BeCM (15) furthest right of four below the seat fuses has:
pin 14 - Cruise control on/off - input
Pin 18 - Power to cruise control ECU , switch telltale and inverter/converter - output
Pin 20 - Road speed (to cruise control ECU) - output

C258 (up to 99my) C1276 (from 99my) 10 pin white (19) the one on the rear of the becm
pin 1 - Cruise control pump supply - output

BeCM communicates with the cruise ECU providing a 12 v square wave speed signal input to the cruise control ECU. The speed signal is derived from the ABS ECU. The BeCM also provides a power input to the cruise control ecu for actuator power from the normally closed brake switch in series between the BeCM and the ecu. When the switch is closed the BeCM provides a 12v supply for actuator operation.


YES Road Speed data is used elsewher ie Instrument Pack, to ATC ECU.

Some interesting reading: http://www.rangerovers.net/forum/7-...1998-cruise-control-fix-may-help-someone.html
 
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Car is 1998 GEMS Petrol. Connectons to Vacuum Pump are all ok. Didn't realise C255 was easy to get at !!

Rave seems to indicate the square wave should be 5V rather than 12v, but will check again.

I ordered an AMR1173 from ebay last night to try. Still need to locate the connector pigtails for a newer AMR5700 to try that fix.
 
When in ABS diagnostics with TestBook there is 5v from each wheel sensor. Is this what you are measuring?
The ABS ECU generates an average of these (all four) to create a road speed signal to the BeCM. The BeCM then outputs a road speed signal to:
Engine Control Module
Cruise control ECU (v8 only)
Instrument Pack.
Air Temp Control (ATC) ECU
In-Car Entertainment.
Electronic Air Suspension(EAS) ECU
Electronic Automatic Transmission (EAT) ECU

On the ABS ECU connector block (35pin)
Pins: 15,16,17,18 are wheel speed sensor (Input)
Pin: 28 BeCM Road Speed signal (Output)
Pin: 29 ECM - rough speed signal. Engine control module) (Output)

Getting interesting
 
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No, the 5V square wave I measured was at the Cruise ECU with everything connected just in case there's a pull-up resistor in the ECU.

I used Tektronix Oscilloscope rather than Voltmeter to check it.

ABS, EAS Motorway Height, etc. all work ok, so I think the speed signals are probably ok.

Could RAVE be wrong about the 5V versus TestBook ? Maybe this could be why so many people have Cruise issues ?

Pete
 
Yes I found that bit, so will check BECM output next. . . . this gets more interesting by the minute :)

Strange that the description talks about 12V square wave, but the Cruise Diag check 3D says "5v with Ignition pos II, and approve 2.5v with wheel turning".

I would expect a 12V square wave should show 6V with wheels turning. . . . the 2.5V expectation ties in with 0-5V square wave signal.

My gut feel is a bad earth somewhere . . . will check E252 behind drivers kick panel.
 
Might be the ECU, so expecting one this weekend. Cannot see how it can be intermittent though. Going outside to check C255 now.
 
C255 earth point did need tightening . . . .but the bolt broke :mad: but managed to locate a suitable chassis ground nearby and installed some extra thick earth wire.

Square wave is definitely 0-5V as per the diagnostic procedure. So either the earlier description about 12V pulses in Rave or the procedure is wrong.

Improving the grounding did not resolve anything either, but I have discovered that the battery ground is somewhat suspect. Good connection from battery to Engine & Starter, but the ground point above Offside Airbag definitely needs improving. Clean it up a bit, but replacement seems in order.

Next step - new Cruise ECU.

Pete
 
Found the problems with my cruise control. Actually there were two issues:

  1. Replaced the ECU with another from Ebay.
  2. Found the brake pedal switch was loose in the mounting . . so went for a drive with the switch hanging out, and then held it in with finger . . . Cruise now works, so next job is new switch.

Also, having replaced the ECU, based on the Audi thread below, I checked the old one again using my USB Microscope. It certainly looks like there are micro-cracks in the capacitor solder joints !!
Definitive solution to repair cruise control module 5GA 004 397-16 - AudiWorld Forums

Pete
 
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