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1999 Range Rover P38 4.0 SE code P1606

Posted By Blue1999P38 12/30/2010 2:27:05 PM
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Blue1999P38
 Posted 12/30/2010 2:27:05 PM
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Hi,
My efforts maybe VERY misguided but I'm trying. I created a log of my repair efforts.
If you have a chance to read the novel below, please let me know if you have any suggestions.
THANKS

09-10-10
My 1999 Range Rover 4.0 SE (GEMS engine) 106,000 miles is stuck in “limp home” mode due to a “Gearbox fault”. I had it at the dealer and was told the next step is to replace the BECM ($2500!) The dealer read codes P0300 Random misfire, P1775 Gearbox fault, P1178 Rich fuel trim, P1316 Misfire, excessive emissions and they said there was no communication with the Trans ECU and the ABS ECU.
DEALER’s repair statement:
found engine fault code P1775 Gearbox fault. comms could not be established with the trans ecu. during diagnosis it was found that comms could not be established with the abs controller. comms were OK with BECM and HVAC. Several faults were found in the HVAC unit but were not investigated at this time. Ran continuity tests on the K and L data lines from the DLC connector to the ABS ECU BECM and the Trans ECU. All tested OK. Removed the center console to check for any terminal corrosion at the trans connector. Checked for operation of the XYZ switch by verifying shifter graphic operation and performing a range change with the Tbox. The data to the instrument pack is not present to display gearbox position. This signal is provided to the instrument pack from the BECM. The next logical step is to replace the BECM in order to start comms. There may also be a fault in the Gearbox however that cannot be determined at this time.

I decided to do the repairs myself and picked the car up from the dealer, the car drove fine with no Gearbox fault. There was a Check engine light on but that has been on for several months. I was a happy camper!

A few weeks later the Gearbox fault reappeared.
It was at this point that I tested the charging system and found it to be a little weak so I replaced the battery, alternator and all cables. The new parts gave me more voltage and better voltage readings but did nothing to cure the fault.
.
Now I have been working on it off and on for over a month or two and I am getting frustrated. I have RAVE and have read a couple hundred pages and studied the Electrical schematics. I have ordered an OBDII reader from Hong Cong on Ebay and will be able to read codes once that arrives. (maybe in January)

The dealer’s information- if it is accurate tells me the Trans ECU had to be communicating with the ECU to throw the codes. (The TCU sends the request to the ECU to illuminate the MIL ) So I am looking for the reason the Trans ECU and the ABS ECU is not communicating thru the OBDII plug and the reason the instrument panel is not receiving the signals from the BECM…and the reason for the codes.

A short list of the work I have done and or items I have inspected to verify they are functional. The majority of the work I have done is to verify that connectors and wires are connected, are not corroded and have continuity.

Replaced battery, alternator, all battery cables and the relays in the under hood fuse box.
Inspected-all of the ground points that I can find (I’m pretty sure I have gotten all of them), checked the fuses in the fuseboxes under hood and on BECM, verified that there is no corrosion in either fuse box, removed BECM cover inspected and cleaned circuit boards in BECM and in the H Gate shift mechanism, removed passenger seat, kick panels, portions of console, window switch pack, covers on B pillars, rocker panels (cover edge of rug at doors), cargo area passenger side deck cover (to access the transmitter for the remote), the panel under the dashboard to access the OBDII plug wiring, both seats lower trim, both air ducts under the seats, the trans ECU connector cover to access the pins from the back of the plug AND under the hood- the battery cover, the ECU cover, the MAF.
11-20-10
A mobile foreign car mechanic met up with me and read the codes. He came up with the same communication problem (the dealer noted) the Trans ECU and the ABS ECU are not communicating with the OBDII plug. He also came up with the same codes.
12-13-10
I cleaned the MAF. I located a vacuum hose that was off the fitting. I think it has something to do with the fuel injection because it originates from a part (modulator?) at the end of the fuel rails near the back of the engine by the coils. I reconnected that vacuum hose to a fitting about 3 inches away on the engine.
12-14-10
I got AutoZone to read the codes (the OBDII reader they use provides generic codes with cryptic descriptions; so it is a guessing game) and it showed P1606 -on various foreign cars that means rough road or engine torque or ABS malfunction, or EEPROM malfunction; P0755 -for BMW it means shift solenoid B rationality check fault and P0750 -for BMW it means shift solenoid A rationality check fault. My thinking is the shift solenoid faults are related to the trans being in “limp home” mode because when it is in that mode, it raises the pressure to the high limit. I also think I MAY HAVE cured the fuel related faults by reconnecting the vacuum hose. I have a hard time trusting the AUTOZONE code reader because it is not specific to the RR.
12-18-10
I TRACED THE WIRING FROM THE Trans ECU for the XYZ switch and confirmed its operation and related voltage in P, R, N, D, 3, 2, 1 and Z to X and Z to Y. So the XYZ switch seems to be OK.
Then I removed the ABS wheel speed sensors and cleaned and reinstalled them (3 were a little dirty and corroded and one was spotless and looked like new!).
12-20-10
Autozone read the codes again and it is a repeat of P1606, P0750, P0755 and a new one P0743. All P07XX codes seem to be related to trans solenoids and the P1606 maybe related to EEPROM malfunction or ABS, or engine torque.
I am thinking I will need to trace the wiring from the OBDII plug back to each ECU for the trans and for the ABS.

I have been told P1606 is labeled as this by LR: P1606 ECM Control Relay O/P Circuit Malfunction. I don't know which components I should check to resolve the P1606 fault.
Any assistance is greatly appreciated.
Thank You!
Robski
 Posted 12/30/2010 2:39:25 PM
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Welcome to the BBA forum BigGrin

Plenty of talk on checking "continuity" but none on "load testing" .


Rob.

Scan it, Smoke it, Scope it....... Don't just poke & hope it © ™ BigGrin
Blue1999P38
 Posted 12/30/2010 7:50:38 PM
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Thank you for the reply. I've always considered myself lacking when it comes to the electronics involved in automotive repair, but I have no choice but to tackle this problem. The dealer has told me he needs to replace a $2500 part (the BECM) to "see if that is the problem". I can't afford to take a chance on guesses.
I am not clear on how to "load test" as well as why I should use that test instead of continuity testing. Again thank you for any assistance and please accept my apologies if I am not proficient enough to discuss electronics with the correct terminology.
thank you
topbloke
 Posted 12/31/2010 11:19:00 AM
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hi, welcome to the site, what Robski is hinting at is although you have tested for continuity on the lines/wires etc this don't mean that it can carry a signal.

 what i mean is say if a wire is a 30 strand wire all of the wires could be broken bar 2 if you were to test for continuity you would find that its okay but it would be incapable of carrying a load. to load test a wire you would need to feed 12 volts down it (isolated from all ecus) then with a bulb or a test probe with a bulb in it check to see if it illuminates at the other end of said wire, I hope this makes sense, Regards TB

Blue1999P38
 Posted 12/31/2010 9:10:06 PM
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thank you. I'll try load testing. my primary question was if anyone had further information on the P1606 fault. Since BBA-reman offers various ecus, I asked on this forum. Again thank you for all of the information.
Happy New Year!
K And R
 Posted 1/1/2011 9:38:30 AM
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B

P1606 was read using an OBD reader so could well be a ghost code. A new code read with T4 (genuine scanner) or similar could bring up a different code.

As you say BBA do lots of ecu.s.

http://www.bba-reman.com/content.aspx?content=range_rover_and_land_rover_discovery_suffering_from_body_electrical_control_module_problems

And

http://www.bba-reman.com/content.aspx?content=Landrover_Transmission_Ecu

May guide you.

Kev.

"If you dont KNOW how it works, don,t try to test or fix it"

Blue1999P38
 Posted 1/1/2011 6:51:55 PM
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thanks. I'm going to call BBA to find out pricing on ECUs. Have a Happy New Year!

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