Alfa Romeo 159 P1642 Engine Trouble Code
What is Alfa Romeo 159 P1642?
With Alfa Romeo 159 P1642, you may drive for several weeks with a malfunctioning MAF sensor, but expect decreased fuel economy and eventual stalling. Shop replacement costs $240–$400 depending on vehicle. The labour is straightforward, with most cost from the part itself.
P1642 on the Alfa Romeo 159
The Alfa Romeo 159 is particularly susceptible to P1642 faults when the engine management unit receives conflicting sensor data. Owners report that P1642 on Alfa Romeo 159 most commonly surfaces after 60,000 miles, especially when routine service intervals have been missed.
Code Information
| Code Type: | OBD-II Powertrain (P) Trouble Code |
| System: | Powertrain |
| Vehicle: | Alfa Romeo 159 |
| Brand: | Alfa |
| Model: | Romeo 159 |
| Code: | P1642 |
P1642 Alfa Romeo 159 Symptoms
Check Engine Light
Illuminated Alfa Romeo 159 dashboard warning
Engine Stalling
Engine stops unexpectedly or misfires
Performance Issues
Reduced power or acceleration on the Alfa Romeo 159
Starting Problems
Difficulty starting the engine
Poor Fuel Economy
Increased fuel consumption on the Alfa Romeo 159
Increased Emissions
Failed emissions test due to P1642
P1642 Code Structure
Understanding what each digit means in the P1642 powertrain trouble code:
| P | 1 | 6 | 4 | 2 |
|---|---|---|---|---|
| Powertrain Code | Fuel And Air Metering | Fuel Temperature Sensor B Circuit Range/Performance | Injection Pump Fuel Metering Control 'B' High | Glow Plug/Heater Circuit 'A' Malfunction |
How to Fix Alfa Romeo 159 P1642
Diagnostic Steps:
Poor running symptoms align with MAP sensor malfunction. In some cases, a faulty MAP sensor will not trigger a code. The issue may represent separate wiring concerns requiring individual diagnosis.
Repair Solution:
Brake switch circuit concerns may involve open or shorted BPP circuits, damaged switches, or misadjustment. Verify stoplight function and follow proper self-test procedures per service manual.
Technical Notes:
P1642 DTC indicating a sensor fault does not always mean the sensor itself is bad. The issue may stem from the systems being monitored or even the sensor wiring. Proper diagnosis is essential.
Alfa Romeo 159 P1642 Repair Cost
ECU software update for the Alfa Romeo 159 to resolve the P1642 calibration bug is performed free of charge at a franchised Alfa dealer under the technical service bulletin programme. Always confirm the ECU part number and current flash version before spending money on sensors.
P1642 Description
P1642 engine trouble code is related to Glow Plug/Heater Circuit 'A' Malfunction.
Main Cause
The primary reason for P1642 OBD-II Engine Trouble Code is: Fuel Temperature Sensor B Circuit Range/Performance.
Common P1642 Misdiagnosis on the Alfa Romeo 159
Some Alfa Romeo 159 models have a known software bug where the PCM flags P1642 after battery disconnection and reconnect. Always perform an ECU adaptation reset and drive cycle before ordering any parts following battery work.
DIY Repair Guide: P1642 on Alfa Romeo 159
When attempting DIY diagnosis of P1642 on your Alfa Romeo 159, a smoke machine test is the gold standard for finding vacuum leaks. Rental tools are available from most auto parts stores for $0–$20/day, or you can fabricate a makeshift tester using a hand vacuum pump and soapy water spray.
Preventing P1642 on the Alfa Romeo 159
For turbocharged Alfa Romeo 159 models, allowing the engine to idle for 60–90 seconds before shutdown after hard driving reduces turbocharger heat soak and prevents the coking of oil that blocks VVT galleries — a known secondary trigger of P1642.
Frequently Asked Questions — Alfa Romeo 159 P1642
A: Almost certainly yes. Most faults that trigger P1642 cause the ECU to operate in open-loop mode or apply overly rich fuel trims, both of which increase fuel consumption by 5–15%. Resolving the fault promptly pays for itself in fuel savings over time.