Last update:

09/10/2005

  Wiring Loom Diagrams

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Fault of the Looms



Several owners have reported experiencing repeated malfunctions of the gearbox - even after having the gearbox and Torque Converter replaced. They have taken it to a main dealer or an autobox repair specialist - only to be told that no faults were present. The following pages are an explanation of the connections throughout the engine management and automatic gearbox looms to enable the owner to carry out his own continuity/fault checks.

Slippage - No error codes

In cases of slippage, that the revs of the engine rise at the same road speed, as if it were a manual gearbox clutch slipping - it is worth checking the MAF. The Mass Airflow Sensor is mounted in the air inlet trunking between the air filter and the inlet manifold. If you check out the page dealing with the EECV,  this reports that symptoms for a fault with the MAF are : Incorrect gearshift scheduling torque converter clutch engages/disengages early/late.  The Comprehensive Component Monitor checks the MAF constantly but sometimes no error codes will be generated if the readings are just under the fault parameters. The torque converter clutch is exactly what makes the gearbox feel that it is slipping - it is because the clutch lock-up has not occurred when it should.

It is fairly simple to remove the housing from the air filter box and the inlet hose, disconnecting it and removing it to the bench. NOTE: Use care with the sensor - it is fragile so do not drop it or submit it to sudden shocks.
See Clean MAF

NOTE: One owner, Oliver, reports that this has cured his symptom of torque converter slip or loss of 4th gear (overdrive). Pete C has also reported that his gearbox was just staring to slip again, (after replacing gearbox and TC last year) and his MAF was filthy. Carb cleaner brought the interior up to a shine again and the slipping stopped immediately.

MAF Test

In some circumstances the MAF can be faulty but does not fail the CCM checks. A Test is available to check for this and this is based on the latest Ford advice.

 

VSS Fault

If the Speedometer is erratic and the automatic gearbox is behaving strangely then suspect the Vehicle Speed Sensor (VSS).  If this is faulty or its connection is poor then it will have a marked effect on gearbox operation, and OBD will report DTCs for this device.  Check the connection to the VSS and replace as necessary.

Loom Faults

Now we come to the more serious symptoms - O/D light flashing, delayed/harsh gearchanges, incorrect gearchanges. Fault codes may include errors with Solenoid C (or #3, depending on tester). Experience has shown that Loom faults often cause different codes that come and go. While some codes clear, others are created and this is a good indicator - a genuine fault would remain until repaired. Codes which appear after heavy rain or washing the car may also lead one to suspect the wiring - but bear in mind the Battery Cover advice

We know from the Revisions page that 24V engines after 01/04/95 had protective sheathing, and that 16V engines suffered from the engine looms chafing on the corner of the cylinder head. One owner experienced a leak which trashed his 24V wiring loom over a period of 2 years and diagnostics remained a puzzle for some time - even using state of the art equipment - until the reason for the gearbox problems was discovered: Wiring Faults
 

ARNITEL

Extended research by FordScorpio.co.uk has traced the problem to faulty Arnitel wiring, used in the engine bay until June 1996, after which production changed to Raychem44 wire, which has proved to be safe. Even so, the Arnitel wire has proved to be reliable on most Scorpio vehicles, just a tiny unlucky minority (9 owners so far) suffering from faulty looms. This should not be confused with another wiring problem for the fuel cut off loom on DOHC models, which caused some confusion until this was recognised as a separate issue effecting all DOHC Scorpios..

 

TESTING

But how can we tell if a wiring loom is causing problems rather than a physical fault inside the gearbox? This needs a detailed knowledge of the colour codes of the wires, the locations of the connectors and all of the pins inside them. Impossible? Not for fordscorpio.co.uk !!

First, we need to know the physical attributes of the loom. We need to understand where it runs from the gearbox to the engine bay and to the EECV.

The picture on the right shows the loom on the top of the A4LDE. In this case the engine is a 24V, but the path is the same. The loom makes two connections to the A4LDE gearbox through two multiplugs, then runs up over the bell housing and thence into the engine bay. The loom is then joined by other connections for the engine sensors (ECT, IAT, TPS, CKP and the HO2S sensors, among others) and then runs from the (facing front of the car) right hand side of the engine to the engine bulkhead, where it terminates in a large square connector beneath the ABS module.

The picture on the right shows this connector, complete with the square nut to clamp it up tight and prevent the entrance of moisture.

The loom on the other side of this connector travels around the bulkhead and enters the cabin through a large grommet, running straight to a large connector on the EECV.

On the face of it, it may seem impossible to trace every pin and track it back inside this loom bristling with wires through the twists and turns in the bulkhead. In fact, testing the whole loom should be quite straightforward.

1. Note that there is no physical break in the loom between the connector C402 on the EECV (from now on, called by it's correct abbreviation, PCM) and the square connector on the engine bulkhead. (C112 and C110)

2. There is no physical break in the loom between the large square connectors C112 or C110 on the engine bulkhead to the connector C604 on the A4LDE, hereafter called by it's correct abbreviation Transmission Hardware Unit (THU)

3. A wire is coloured the same in the entire loom from the connection on the PCM (C402) to the multiplug on the THU (C604)

4. Wires connecting sensors which operate at low signal voltages are coated in gold and protected by a special grease which does not contain lithium (which would lift the gold plating and cause problems) So if you open a connection and there are some gold and some tin connections, you will know that the gold ones are critical signal wires.

5. A simple circuit test is insufficient for this diagnostic - it is not sensitive enough to detect voltage drop and leakage across wires. A digital multimeter is essential for this task. They may be obtained quite cheaply from Halfords.

If follows that, since a pin in the PCM connector C402 has no physical break between that and the bulkhead connector C112, we can make continuity checks between the corresponding pins. Leakage checks would also be useful - connect to one pin on C402 and check all the pins in C112 - if a voltage is detected on a pin other than the correct one this would indicate a break in insulation. This can either be investigated further and repaired (knowing which colour wire to look for inside the loom) or by replacing the loom altogether. Similarly, the engine loom can be checked between the bulkhead connector C402 and the THU connector C604.

Using the data very kindly supplied by Ford (Europe) I have prepared tables of connections at each point: C402, C112, and C604 and the corresponding colour code and usage of the wire. Since several owners of 16V cars have experienced doubts about their loom integrity, I have started with their coding. Others will follow, and will have their own pages selected from the menu on the left.

Gaining access to the connections

So where are they?

C402

. Ford (Europe)

The PCM is behind the glove box. This is removed by pressing out the supports and lowering the glove box. Remove under trim fasteners and remove the under trim panel. The PCM is the larger unit secured into the bulkhead with rivets. The PCM connector C402 can be unbolted and pulled away from the PCM.

C112 and C110


. Ford (Europe)


The bulkhead connector C112 is, as already stated, on the left hand engine side bulkhead beneath the ABS module. The single bolt through the top is released and the halves of the connector separated. Bear in mind that when the two faces are upward they are mirror images of each other - the top two holes on the lower half are 21 and 27, while pins on the upper half are 27 and 21. Some models have two connectors, the second being identical in pin configuration, and is called C110. Most gearbox functions pass through C112, and engine wires through C110.

C604


. Ford (Europe)


The HTU multiplug C604 is mounted on the right hand side of the gearbox just forward of the transmission selector fulcrum. It may be reached if there is enough room for an arm - but remember that if the connector is pulled off it will need to be replaced and this should be borne in mind. Two locking lugs need to be released at the same time that the multiplug is pulled free. DO NOT pull on the wire - this may result in dislodging the terminals inside. In the event that some terminals are showing corrosion, these can be repaired using a repair kit available from a Ford Main Dealer. If a terminal is gold-plated, it must be repaired using another gold terminal and lithium based greased must not be used. The repair kit contains the correct special grease. This grease is Myogel 760A Finis 5 030 186.

It may be necessary to lower the gearbox slightly, and on some models (24V especially) the exhaust may need to be removed first. I suggest that the whole operation will be much easier with two operators, one at each end to enable the tests to be carried out efficiently.

Complete wiring details for the Scorpio in Acrobat form are shown here - note: this link takes you away from www.fordscorpio.co.uk.

Now use the links on the left corresponding to your engine - and good luck!



EricR

 

 

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