DTC P1631 Immobilizer Invalid Response

Diagnostic Trouble Code (DTC) P1631

Immobilizer Invalid Response





Circuit Features



  • The Engine Control Module (ECM) acts as the nerve center of the fuel injection system.
  • The ECM monitors the information from various sensors throughout.
  • The ECM also regulates the systems that are likely to affect vehicle performance adversely.
  • The ECM which carries out the diagnostic function of the system is able to identify operational problems, caution the driver through the Malfunction Indicator Lamp (MIL) (Check Engine), and store a Diagnostic Trouble Code (DTC) or DTCs which identify the problem areas to assist the technician in repairing the flaws.
  • The ECM also obtains inaccurate message identification.








When will DTC set?


Task boosted after DTC sets

When will DTC clear?

DTC sets when:

1) Ignition switch remains ON.

1) The Malfunction Indicator Lamp (MIL) will not be seen to glow.

1) A Scan Tool can be used to remove all DTCs.


2) Wrong immobilizer message obtained.

2) The ECM will begin to record operating conditions when the diagnostic fails.


2) A history DTC will unset after 40 repetitive and flawless warm-up cycles.

3) Immobilizer option has been selected.


3) This data will be stored in the Freeze Frame and Failure Records will be boosted.


3) De-linking the ECM battery feed for more than 10 seconds.

4) ECM release time window expired.

4) A history DTC is stored.


5) Vehicle Speed Sensor (VSS) < 512 km/h.









DTC P1631 - Immobilizer Invalid Response



What to do




Carry out an EOBD system check.


Job done?

Look up

Step 2

Go to

"On-Board Diagnostic System Check"


  1. Switch OFF the ignition.
  2. Change the ECM.

Task done?

Look up

 Step 3



  1. Unset all DTCs taking a Scan Tool.
  2. Start the engine.
  3. Let the engine idle at normal operating temperature.
  4. Control the vehicle within the Conditions for setting this DTC as given in the supporting text.

Do you see the scan tool showing that this diagnostic has been run and passed?


Look up

Step 4

Look up

 Step 2


Look up if any additional DTCs are set.


Do you see any DTCs shown that have not been diagnosed?

Go to

Applicable DTC table

The system of your vehicle is fine