Specific Symptom Diagnosis
Specific Symptom Diagnosis
The following Symptom/Complaint diagnostic procedures should allow for easy diagnosis of a Transfer Gearbox Control System problem. The procedures detailed in the "Diagnostic Checks" will aid in diagnosis.
CAUTION: In order to avoid damaging a replacement TCU, check the shift control motor before energizing the system (Check #4).
Symptom/complaint:
- No range change
- Burning odor
- H-gate lights on, flashes if shift requested
- "Select Neutral" warning (possible)
Description:
The output drive circuits in the TCU may have failed. The shift control motor may have failed.
Repair:
1. Check TCU output to shift control motor (Check #2).
2. Check Fuse No. 4 in BeCM.
3. Inspect Shift control motor (Check #4).
Symptom/complaint:
- No range change
- Both sides of H-gate dim/out
- Poor shifting of automatic transmission in high range (possible).
- No response to range change requests.
Description:
TCU may be inoperative or lack ignition feed.
Repair:
1. Check for blown fuse Position No. 6.
2. Check ignition feed to TCU.
3. If 1 and 2 check out, replace TCU.
Symptom/complaint:
- MIL illumination.
Description:
Code P1701- Transfer Gearbox line fault.
Repair:
1. Fill out DTCR and FAX to LRNA.
2. Check speed sensor resistance. Resistance should be approximately 1,400 ohms.
3. Read Shift Control Motor encoder switches (Check #3).
4. If motor encoder switch information does not match motor position, replace shift control motor.
Symptom/complaint:
- MIL illumination.
Description:
Code P1703- Transfer Gearbox line open circuit line fault.
NOTE: If code 1317 occurs with code 1703, refer to Operation Pride article 1-03 (TIB 19/11/96/US) for further diagnosis.
Repair:
1. Fill out DTCR and FAX to LRNA.
2. Check if power supply has been interrupted to the TCU (e.g., battery replacement, blown fuse or a loose battery terminal causing an intermittent open circuit). Even if the power is only briefly interrupted the GEMS ECM will "wake-up" before the TCU and set a 1703 code.
3. Check circuit between TCU and GEMS ECM for open circuits.
NOTE: In the event of codes 1703 and 1708, the circuit and connector C-603 should be checked very closely. The inability of the TCU to move the transfer gearbox into high range is flagged over a fault output line (C-603 Pin-28). It is highly unlikely that these codes are set because of a TCU failure. Do not replace a TCU in an attempt to resolve these codes without confirming that a hard fault exists with the TCU. Confirm the problem by substituting the suspect TCU into a known good vehicle.
Symptom/complaint:
- MIL illumination.
Description:
Code P1708- Transfer Gearbox line short circuit fault.
Repair:
1. Fill out DTCR and FAX to LRNA.
2. Check circuit between TCU and GEMS ECM for short circuits.
Symptom/complaint:
- Vehicle shifts poorly in high range.
Description:
The High Range Status line should be near GND (0V) when the vehicle is in high range, informing the TCM that the vehicle is in high range. If the high range status line is near battery power, when the vehicle is in high range, the TCM will enable the incorrect shift strategy.
Repair:
1. Ensure that the vehicle is physically in high range.
2. Check if the High side of the H-gate is lit (it should be brighter than the low side) when in high range.
3. If it is lit properly, refer to Automatic Transmission Diagnostics.
4. If it is not lit, check the connection at C603 pin 35.
5. Check the motor encoder switches for appropriate motor position (Check #3). If the switches do not indicate high range, the TCU will not pull down the High Range status line to near 0V and the TCM will select the shift strategy for low range.
6. If the encoder switches do not indicate high range, replace the shift control motor and check the vehicle for proper operation (Check #1).
7. If the high range status line and connections are good, replace the TCU.
Symptom/complaint:
- Vehicle shifts poorly in Low Range.
Description:
The High Range Status line should be near battery voltage when the vehicle is in Low Range, informing the TCM that it is in low range. If the high range status line is near GND (0V) the TCM will enable the incorrect shift strategy.
Repair:
1. If the High side of the H-gate is dim, check the operation of the H-gate switch with TestBook (Check #5).
2. If TestBook Test indicates a malfunction, check the circuit between H-gate connector C617 pin 8 and TCM C601 pin 46.
3. If the H-gate is bright in both ranges, check for a short to ground in the High Range Status line.
Symptom/complaint:
- "Select Neutral" warning displayed in Message Centre.
Description:
Warning displayed if gear was selected before shift was completed.
Repair:
1. Inspect operation of TCU (Check #1).
2. Pause in neutral to allow range change.
Symptom/complaint:
- Cruise control inoperative
Description:
The high range status line should be low (near 0V) while the vehicle is in high range. If it is high (near battery voltage) the BeCM thinks that the vehicle is in low range and cruise control operation is not enabled.
Repair:
1. If the High side of the H-gate is lit, the problem is not TCU related, check elsewhere for the problem.
2. Check the connection at C603 pin 35. Repair as necessary.
3. Check the shift control motor position encoder switches (Check #3). If they do not indicate high range, the TCU will not pull the high range status line down near 0V and the BeCM will not enable the cruise control system. Repair as necessary.
4. If H-gate is not illuminated properly, check the motor position switch pins at the TCU. If no fault is found, replace the TCU.
Symptom/complaint:
- "Transfer Neutral" displayed in Message Centre
Description:
Displayed if Neutral range status line is low (near 0V). Transfer neutral is activated by installing fuse in position No. 11.
Repair:
1. Check that a fuse has not been mistakenly inserted in position No. 11.
2. Check Neutral status line for short to ground.
3. Check for open circuit to BeCM.
Symptom/complaint:
- "Slow Down" warning displayed in Message Centre.
Description:
NOTE: The BeCM uses a speed signal from the ABS system to judge vehicle speed.
Warning is displayed if the BeCM determines vehicle speed is in excess of 5 mph (8 kph). Early 1995 MY Range Rover BeCM software may generate the 'Slow Down' message if the range change did not occur within 4 seconds. This was corrected by mid 1995 MY.
Repair:
1. Check ABS system.