P1626 theft code issue

STEVE LAMB

MEMBER
2003 CHEVROLET S-10
4.3L
V6
4WD
AUTOMATIC
65,000 MILES

Vehicle cranks, won't start. I checked fuel pressure, good, checked spark, good. Purchased engine diagnostic tool and getting P1626 code. Code indicates issue with theft system and PCM not getting correct code from BCM, which the PCM cuts off fuel.

At one point I bypassed the theft system with the jumper wire, was able to do the relearn and after a week was successful getting it started. The security light remained on however. I then replaced the spider injection system, which I disconnected the battery. After installing the injectors, the truck started right up. The next day, it would not start. I did the relearn, and nothing. I removed the jumper and relearned, and no start.

That's when I purchased the diagnostic tool (Autel MK808BT), and discovered the P1626. Subsequently, I replaced the ignition wire harness, the ignition housing (which contained the passlock system), the BCM, and the PCM. All the relearns seem to be successful.

Checked the security system using the Autel, and the live data is indicating everything is working fine. I'm getting my 5 volts reference through the passlock, then when the key is turned on the voltage drops under 5 volts like it is supposed to do. The key code indicates passed with a "Valid Code 10". Live engine data shows the engine is turning with rpm's around 110 or so (so I don't suspect crank or cam sensor issues).

I then replaced the BCM, completed the relearn and no codes with the BCM, but still getting the P1626 through the PCM. I even tried going back to the old ignition harness with the bypass wire (no success). I then removed the bypass wire and installed two resistors that bypass wire that simulated the resistance of the key. No success.

Reinstalled the new harness again, replaced the PCM, complete the relearn, and I am still exactly where I was. The only think left that I have been reading about is possible ground issue/wiring issue between the BCM and PCM?

Would love some advice.

Thanks!
Steve

1 Reply

ASEMASTER6371

MECHANIC
52,797 POSTS

Good morning,

Did you have the PCM and BCM flashed to your VIN number?

I posted the description below for the code.

Did you follow this information?

Roy

DTC P1626

CIRCUIT DESCRIPTION
The control module communicates with other modules using the Class 2 Serial Data circuit. The vehicle theft deterrent (VTD) body control module (BCM) sends a vehicle security password to the powertrain control module (PCM), via the Class 2 Serial Data circuit, after the BCM has sensed the proper operation of the ignition switch and lock, and determined that the switch and lock have not been tampered with. If this password matches the password stored in the PCM, fuel will be enabled. If the BCM does not send a password, or if the PCM does not receive it, the vehicle will not start, or it may start and stall. This will set a DTC P1626 in the PCM memory. If communication is lost after receiving the password, the VTD Passlock system will go into Fail Enable, set a U1192 in the PCM memory, and the engine will continue to run. This will allow the engine to restart on future ignition cycles but may set a DTC P1626 as the engine is started. If the battery is disconnected or the codes are cleared, the vehicle will lose its Fail Enable status and will not start until communication is re-established.

CONDITIONS FOR RUNNING THE DTC
- The vehicle theft deterrent (VTD) system is enabled.
- The fuel enable decision point has been reached, or the engine is cranking.

CONDITIONS FOR SETTING THE DTC
The powertrain control module (PCM) has not established communications with the body control module (BCM) and has not received a valid password before the fuel disable decision point was reached.

ACTION TAKEN WHEN THE DTC SETS
- The powertrain control module (PCM) stores the DTC in history after the first failure but will not illuminate the malfunction indicator lamp (MIL).
- The powertrain control module (PCM) records the operating conditions at the time the diagnostic fails. The PCM stores the failure information in the scan tools Freeze Frame/Failure Records.

CONDITIONS FOR CLEARING THE MIL/DTC
- A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles.
- A warm-up cycle occurs when the coolant temperature has risen 22°C (40°F) from the startup coolant temperature and the engine coolant temperature exceeds 70°C (160°F) during the same ignition cycle.
- Use the scan tool Clear Information function.

DIAGNOSTIC AIDS

IMPORTANT: Do not clear DTCs unless directed by a diagnostic procedure. Clearing DTCs will also clear valuable Freeze Frame and Failure Records data.

- Check for published service bulletins relating to exhibited symptoms or component operation.
- Inspect all related wiring and connections including the powertrain control module (PCM) and body control module (BCM) connections. These may cause an intermittent malfunction.
- If the Class 2 Serial Data circuit is shorted to ground or shorted to voltage, then all systems connected to the serial data circuit will not be able to communicate properly. Systems capable of storing loss of communications DTCs, or the DTCs with the letter "U" as a prefix, will have these codes stored in their memory. If a DTC U1192 is stored in the PCM memory along with the P1626, then a fault occurred at some point after the PCM received the correct password. The BCM must also be checked for intermittent operation due to a loss of power or ground to the module itself. After repairing the cause of DTC 1626, clear all DTCs from the systems capable of storing this DTC and DTC U1192.
- The VTD Passlock parameters can be monitored in the PCM under engine data 2, display with a scan tool.
- The scan tool Diagnostic Circuit Check can be used to:
- Monitor the Class 2 Serial Data circuit for modules which have been or are communicating.
- Monitor for loss of communications DTCs with the letter "U" as a prefix: U1001-U1199.
- Clear loss of communication DTCs. When a Clear Codes command is issued, all codes, Freeze Frame and Failure Records information is cleared.
- The scan tool Class 2 Message Monitor will show the status of each module on the Class 2 circuit. A status of Active indicates that the module is communicating with the scan tool. An Inactive status indicates that the module previously communicated with the scan tool, but is not communicating currently. The inactive status will only appear if the loss of communication occurs while on the Message Monitor screen. If a module is not listed at all, then the missing module never successfully established communications with the scan tool or lost communication while on another screen. Refer to Scan Tool Does Not Communicate with Class 2 Device in Data Link Communications for the complete Class 2 data link to determine if there are any unlisted modules. See: Information Bus > Symptom Related Diagnostic Procedures

An intermittent may be caused by any of the following conditions:
- A poor connection
- Rubbed through wire insulation
- A broken wire inside the insulation

Thoroughly inspect any circuitry that is suspected of causing the intermittent complaint.