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Home/Acura/MDX/Acura MDX I (2000-2006)/Repair manual/Door Locks & Anti-Theft Systems/Immobilizer System
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Immobilizer System Acura MDX I

Door Locks & Anti-Theft Systems 13 illustrations ~2105 words

Scheme 2

Scheme 2: Component Location Index
Scheme 2: Component Location Index

System Description

The vehicle is equipped with an immobilizer system (type ill) that will disable the vehicle unless a programmed ignition key is used.

This system consists of a transponder located in the ignition key, an immobilizer control unit-receiver, an indicator light, and the PCM.

When a programmed key is inserted in the ignition switch and turned to the ON (II) position, the immobilizer control unit-receiver sends power to the transponder in the ignition key. The transponder then sends a coded signal back through the immobilizer control unit-receiver to the PCM, and the PCM enables the fuel and ignition systems. The transponder codes are embedded in the immobilizer control unit-receiver (fixed code). A handshake between the PCM and the immobilizer control unit-receiver is required at the PCM repair and replacement, and all keys are required at the immobilizer control unit-receiver repair and replacement.

Scheme 3

Scheme 3: System Description
Scheme 3: System Description

Scheme 4

Scheme 4
Scheme 4
  1. If a programmed key has been used, the immobilizer indicator light will come on for about 2 seconds, then go off. When the ignition switch is turned OFF, the indicator will blink for about 5 seconds to signal that the unit has been set correctly, then the indicator will go off.
  2. If the a non-programmed key has been used whose code was not received or recognized by the unit, the indicator light will come on for about 2 seconds, then it will blink until the ignition switch is turned OFF.

Scheme 5

Scheme 5: Circuit Diagram
Scheme 5: Circuit Diagram

Scheme 6

Scheme 6: Troubleshooting
Scheme 6: Troubleshooting

Scheme 7

Scheme 7
Scheme 7

Scheme 8

Scheme 8
Scheme 8

Scheme 9

Scheme 9
Scheme 9

Scheme 10

Scheme 10
Scheme 10

Scheme 11

Scheme 11
Scheme 11

Scheme 12

Scheme 12
Scheme 12

Scheme 13

Scheme 13
Scheme 13
  1. Turn the ignition switch ON (II) with a programmed key.
  2. Check to see if the immobilizer indicator comes on. Does the indicator come on? YES - Go to step 3. NO - Go to step 12 .
  3. Check the immobilizer indicator operation. Does the indicator come on for 2 seconds, then go off? YES - Go to step 4. NO - Go to step 6 .
  4. Try to crank the engine. Does the starter motor operate? YES - Go to step 5. NO - Check the starter motor.
  5. Try to start the engine. Does the engine start? YES - If available, check the Status Log in the Immobilizer info with the HDS (see «STATUS LOG»(/acura/mdx/i-2000-2006/remont/door-locks-anti-theft-systems/#immobilizer-system__status-log) ). If the Status Log is not available, the immobilizer system is OK at this time. NO - Go to step 24 .
  6. Check to see if the immobilizer indicator comes on and blinks. Does the indicator blink? YES - Go to step 24 . NO - Go to step 7.
  7. Disconnect the 7P connector from the immobilizer control unit-receiver.
  8. Check to see if the immobilizer indicator goes off. Does the indicator go off? YES - Substitute a known-good immobilizer control unit-receiver and/or PCM. NO - Go to step 9.
  9. Turn the ignition switch OFF.
  10. Remove the gauge control module and disconnect its connectors (see «GAUGE ASSEMBLY REPLACEMENT»(/acura/mdx/i-2000-2006/remont/gauges-instrument-panels/#gauges) ).
  11. Check for continuity between the immobilizer control unit-receiver 7P connector No. 5 terminal and body ground. Is there continuity? YES - Repair a short in the wire. NO - Faulty immobilizer indicator, replace the gauge control module.
  12. Try to start the engine. Does the engine start? YES - Go to step 13. NO - Go to step 18 .
  13. Turn the ignition switch OFF.
  14. Disconnect the 7P connector from the immobilizer control unit-receiver.
  15. Check for voltage between the immobilizer control unit-receiver 7P connector No. 7 (+B) terminal and body ground. Is there battery voltage? YES - Go to step 16. NO - Faulty No. 13 (7.5 A) fuse in the passenger's under-dash fuse/relay box. If the fuse is OK, check for an open in the wire between the immobilizer control unit-receiver and passenger's under-dash fuse/relay box.
  16. Remove the gauge control module and disconnect its connectors (see «GAUGE ASSEMBLY REPLACEMENT»(/acura/mdx/i-2000-2006/remont/gauges-instrument-panels/#gauges) ).
  17. Check for continuity between the immobilizer control unit-receiver 7P connector No. 5 terminal and gauge assembly connector B (30P) No. 9 terminal. Is there continuity? YES - Faulty immobilizer indicator, replace the gauge assembly. NO - Repair an open in the wire.
  18. Turn the ignition switch OFF.
  19. Disconnect the 7P connector from the immobilizer control unit-receiver.
  20. Turn the ignition switch ON (II).
  21. Check for voltage between the immobilizer control unit-receiver 7P connector No. 6 terminal and body ground. Is there battery voltage? YES - Go to step 22. NO - Faulty No. 92 (7.5 A) in the auxiliary fuse holder 2. If the fuse is OK, check for an open in the wire between the immobilizer control unit-receiver and auxiliary fuse holder 2.
  22. Turn the ignition switch OFF.
  23. Check for voltage between the immobilizer control unit-receiver 7P connector No. 1 and No. 6 terminals. Is there battery voltage? YES - Substitute a known-good immobilizer control unit-receiver and recheck. NO - Repair an open in the wire or poor ground (G101).
  24. Turn the ignition switch OFF.
  25. Connect the HDS to the data link connector.
  26. Turn the ignition switch ON (II).
  27. Look at the System Check in the Immobilizer Info with the HDS (see «SYSTEM CHECK»(/acura/mdx/i-2000-2006/remont/door-locks-anti-theft-systems/#immobilizer-system__system-check) ). Is the immobilizer system normal? YES - Go to symptom troubleshooting (see «SYMPTOM TROUBLESHOOTING INDEX»(/acura/mdx/i-2000-2006/remont/auxiliary-emission-control-systems/#fuel-and-emissions-systems__symptom-troubleshooting-index) ). NO - Go to step 28.
  28. Verify the System Check display on the HDS for the following information: Harness short from the PCM to the immobilizer unit. (S-net line short) The communication was not good between the PCM and the immobilizer unit by the battery voltage low. The communication was not good between the immobilizer unit and the PCM by influence of some noise. Immobilizer unit failure PCM failure Does the HDS display any of the above information? YES - Go to step 29. NO - Go to step 33 .
  29. Turn the ignition switch OFF.
  30. Disconnect the 7P connector from the immobilizer control unit-receiver.
  31. Disconnect the PCM connector B (56P).
  32. Check for continuity between the immobilizer control unit-receiver 7P connector No. 2 terminal and body ground. Is there continuity? YES - Repair a short in the wire. NO - Substitute a known-good immobilizer control unit-receiver and/or PCM.
  33. Verify the System Check display on the HDS for the following information: Blown fuse Harness open from the PCM and the immobilizer unit. The communication was not good between the PCM and the immobilizer unit by battery voltage low. The communication was not good between the immobilizer unit and the PCM by influence of some noise. Immobilizer unit failure PCM failure Does the HDS display any of the above information? YES - Go to step 34. NO - Check the Possible Failures shown on the System Check display (see «SYSTEM CHECK»(/acura/mdx/i-2000-2006/remont/door-locks-anti-theft-systems/#immobilizer-system__system-check) ).
  34. Turn the ignition switch OFF.
  35. Disconnect the 7P connector from the immobilizer control unit-receiver.
  36. Disconnect the PCM connector B (56P).
  37. Connect the immobilizer control unit-receiver 7P connector No. 2 terminal and body ground with a jumper wire.
  38. Check for continuity between the PCM connector B (56P) No. 41 terminal and body ground. Is there continuity? YES - Substitute a known-good immobilizer control unit-receiver and/or PCM. NO - Repair an open in the wire.

System Check

  1. Connect the HDS to the data link connector.
  2. Turn the ignition switch ON (II).
  3. Monitor the System Check in the Immobilizer Info with the HDS.
  4. If the HDS displays the "Immobilizer system is normal", the immobilizer system is OK. If the HDS displays any other messages, check as follows: SYSTEM CHECK Status Log No. System Check Possible Failures A-1 Immobilizer system is not normal This key is not registered in the immobilizer unit. Try to register keys by using "KEYS". The communication was not good between the antenna and the immobilizer key by influence of metal such as key chains. The communication was not good between the antenna and the immobilizer key by battery voltage low. A-2 Immobilizer system is not normal Intermittent interruption between transponder and immobilizer unit. The immobilizer key type is different. It is not for this vehicle but for another one or for other company's one. Key failure (transponder failure) The communication was not good between the antenna and the immobilizer key by influence of metal such as key chains. The communication was not good between the antenna and the immobilizer key by battery voltage low. A-3 Immobilizer system is not normal The ignition switch was turned on with a non-immobilizer key. The immobilizer key type is different. It is not for this vehicle but for another one or for other company's one. Key failure (transponder failure) The communication was not good between the antenna and the immobilizer key by influence of metal such as key chains. The communication was not good between the antenna and the immobilizer key by battery voltage low. Immobilizer unit failure B-1 Immobilizer system is not normal The PCM was not registered. Try to register the PCM by using "REPLACE PCM". The communication was not good between the PCM and the immobilizer unit by battery voltage low. The communication was not good between the immobilizer unit and the PCM by influence of some noise. B-2 Immobilizer system is not normal The PCM was not registered. Try to register the PCM by using "REPLACE PCM". The communication was not good between the PCM and the immobilizer unit by battery voltage low. The communication was not good between the immobilizer unit and the PCM by influence of some noise. D-1 Immobilizer system is not normal Harness short from the PCM to the immobilizer unit. (S-net line short) The communication was not good between the PCM and the immobilizer unit by battery voltage low. The communication was not good between the immobilizer unit and the PCM by influence of some noise. Immobilizer unit failure PCM failure D-3 Immobilizer system is not normal Blown fuse Harness open from the PCM to the immobilizer unit. The communication was not good between the PCM and the immobilizer unit by battery voltage low. The communication was not good between the immobilizer unit and the PCM by influence of some noise. Immobilizer unit failure PCM failure

Status Log

If you suspect there is a immobilizer system problem, check the status log.

Note. The status log may not be available for all models. If you have an updated immobilizer control unit-receiver ('03-04 models) or on '05-06 models, the status log should be available.

  1. Connect the HDS to the data link connector.
  2. Turn the ignition switch ON (II).
  3. On the HDS screen, select Honda systems, select immobilizer set-up, select immobilizer information, then select status log.
  4. Check the status log count. Troubleshoot the status with the highest count first. If no counts are listed, the immobilizer system is OK. Continue with normal symptom troubleshooting. STATUS LOG Status Log No. Detected Item Probable Cause A-1 KEY CODE MISMATCH (Code format normal, but code data is mismatch) The key was not registered Interference from metal such as key chains Low battery voltage A-2 KEY CODE MISMATCH (Code format failure) Ignition switch was turned on with another type of immobilizer key or aftermarket key Interference from metal such as key chains Low battery voltage A-3 KEY CODE MISMATCH (No key code or non-immobilizer key) Ignition switch was turned on with another type of immobilizer key or aftermarket key Interference from metal such as key chains Low battery voltage Key failure Immobilizer control unit-receiver failure B-1 PCM CODE MISMATCH (Code format normal, but code data is mismatch) PCM was not registered correctly Low battery voltage Poor or loose terminal connections at the immobilizer control unit-receiver Communication line electrical noise B-2 PCM MISMATCH (Code format failure) PCM was not registered correctly Low battery voltage Poor or loose terminal connections at the immobilizer control unit-receiver Communication line electrical noise D-1 SECURITY-NET LINE PROBLEM (Short to ground) Low battery voltage Poor or loose terminal connections at the immobilizer control unit-receiver and the PCM Communication line electrical noise D-3 SECURITY-NET LINE PROBLEM (Open line or PCM failure) Open or short in the harness from the PCM to the immobilizer control unit-receiver Low battery voltage Poor or loose terminal connections at the immobilizer control unit-receiver and the PCM Communication line electrical noise

Scheme 14

Scheme 14: Immobilizer Control Unit-Receiver Replacement
Scheme 14: Immobilizer Control Unit-Receiver Replacement
  1. Remove the driver's dashboard lower cover (see «DRIVER'S DASHBOARD UNDER COVER REMOVAL/INSTALLATION»(/acura/mdx/i-2000-2006/remont/exteriorinterior-trim/#dashboard) ).
  2. Remove the steering column covers (see «STEERING COLUMN REMOVAL AND INSTALLATION»(/acura/mdx/i-2000-2006/remont/manual-power-steering/#power-steering-system__steering-column-removal-and-installation) ).
  3. Remove the gray connector lock (A) from the 7P connector.
  4. Remove the two screws and the immobilizer control unit-receiver (C) from the ignition key cylinder (D).
  5. Install the immobilizer control unit-receiver in the reverse order of removal.
  6. After replacement, rewrite the unit with an HDS, then check the immobilizer system.

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