U1008 on 2017-2019 Alfa Romeo Giulia: LIN 1 Bus Fault Causes and Fixes

What's Unique About the 2017-2019 Alfa Romeo GIULIA

On the Giulia and its platform-mate, the Stelvio, the U1008 code is very specifically tied to the auxiliary water pump circuit for the turbocharger's charge air cooler. While many cars use LIN networks, the Giulia's frequent association of U1008 with a failing pump relay is a distinct and well-documented pattern among owners. This isn't just a random network glitch; it's a known weak point that can cause sluggish performance without illuminating a check engine light. 🎬 Watch: How this relay fix restores lost engine power. This leads owners to notice the power loss before any warning appears on the dash, and the code is often found stored in memory during a scan.

Diagnostic Flowchart

Tap your situation to follow the diagnostic path that matches what you're seeing on this vehicle.

Symptoms You May Notice

• Noticeable loss of engine power or sluggish performance, especially at higher RPMs or during aggressive driving.
• No Check Engine Light (the code is often stored without illuminating the MIL).
• In some cases, the Malfunction Indicator Lamp (MIL) may be illuminated, especially if accompanied by other codes like P026E.
• A high-pitched buzzing sound from under the dashboard or engine bay, which could indicate an electrical issue with the auxiliary pump circuit.

Most Likely Causes

1. Faulty Auxiliary Water Pump Relay 🔴 High Probability Forum discussions among owners on platforms like GiuliaForums.com and Reddit suggest a very high failure rate for the original relay that controls the charge air cooler's auxiliary water pump.
   How to confirm: Scan the vehicle for codes. The relay is located in a small fuse/relay box behind the passenger-side headlight on US models. 🎬 See this walkthrough for locating and replacing the relay. Swap the suspect relay with a known-good relay of the same type from a less critical circuit, such as the one for the headlamp washers. Clear codes and test drive. If the U1008 code does not return, the relay is bad.
   Typical fix: Replace the faulty relay with a new, often superseded, part. The original Mopar part number is 06106094AA. This has been superseded by part number 6106093AA.
   Est. part cost: $10-$25
2. Outdated PCM Software 🟡 Medium Probability Alfa Romeo has issued several Technical Service Bulletins (TSBs), such as #18-045-23, that involve reprogramming the Powertrain Control Module (PCM) to address a group of codes, including U1008. The update can change the diagnostic strategy or the pump's operational parameters.
   How to confirm: A dealership or a properly equipped independent shop can check the current software version of the PCM against the latest version available from Alfa Romeo using a tool like wiTECH.
   Typical fix: Reprogram the PCM with the latest software version as per the relevant TSB. This is typically a dealer-performed action. TSB 18-045-23 specifically mentions an update to the 'Turbo coolant pump after run duration and on-off strategy' to improve O-ring durability.
   Est. part cost: $0 (if under warranty) or $150-$300 (dealer labor)
3. Wiring Harness Issue ⚪ Low Probability While not exceptionally prone, the engine bay is a harsh environment. Wires can chafe or connectors can become loose or corroded over time, especially around the relay box or the pump itself.
   How to confirm: Visually inspect the wiring going to the auxiliary water pump and its relay. Check for breaks, corrosion, or shorts in the single LIN bus wire. A multimeter is needed to check for continuity from the PCM to the pump and to check for shorts to power or ground.
   Typical fix: Repair the damaged section of the wiring harness or clean/replace the affected connector.
   Est. part cost: $5-$50

Rare But Worth Checking

• Failed Auxiliary Water Pump: While the relay is far more common, the pump itself can fail. It is an electrical component on the LIN bus, and an internal failure could disrupt communication, triggering U1008. If replacing the relay and checking the wiring doesn't solve the issue, the pump becomes the next suspect. Symptoms can include coolant leaks or whining noises.

Diagnosis Steps

1. Scan the Powertrain Control Module (PCM) for stored trouble codes using an OBD-II scanner. Note if U1008 is present, even without a Check Engine Light.
2. Check for the presence of related codes, especially P026E, which pinpoints the charge air cooler pump circuit.
3. Locate the relay box behind the passenger-side headlight (for US models). It's a small black box.
4. Identify the auxiliary water pump relay. It is often the same type as the headlamp washer relay in the same box.
5. As a simple diagnostic test, swap the pump relay with an identical relay from a non-critical system (like the headlamp washer). Ensure the part numbers on the relays are identical.
6. Clear the codes using the scanner and perform a thorough test drive, trying to replicate the conditions where power loss was noticed.
7. If the code U1008 does not return and performance is restored, the original relay is faulty and must be replaced with a new part (Mopar #6106093AA).
8. If the code returns, proceed with electrical diagnosis. Using a multimeter set to DC Volts, probe the LIN bus wire at the auxiliary pump connector. A healthy, communicating LIN bus will toggle between approximately 1V and battery voltage (around 12V).
9. If the LIN bus voltage is stuck high (approx. 12V) or low (0-1V), or is missing entirely, inspect the wiring harness for opens, shorts to ground, or shorts to power between the PCM and the pump.
10. Check for a solid ground connection at the main engine bay ground point, located on the upper frame rail near the passenger side hood lock.
11. If wiring and the relay are confirmed good, the auxiliary water pump itself may have an internal electronic fault, requiring replacement.
12. Finally, check with an Alfa Romeo dealer if your vehicle's PCM software is up to date, as TSBs like #18-045-23 exist to address this code.

Parts You'll Likely Need

• Auxiliary Water Pump Relay (OEM #6106093AA) — This is the most common failure point for the U1008 code on this vehicle, as widely documented in owner forums. The original part number was 06106094AA, which has been superseded by 6106093AA.
  Trusted brands: Mopar
  OEM price range: $15-$25
  Aftermarket price range: $10-$20
• Auxiliary Water Pump (OEM #505528600) — If the relay and wiring are good, the pump itself is the next most likely component to have failed. An internal electronic fault in the pump can disrupt LIN bus communication.
  Trusted brands: Mopar, Bosch
  OEM price range: $150-$250
  Aftermarket price range: $100-$180

Related Codes That Often Appear With This One

• P026E — This code directly translates to 'Charge Air Cooler Coolant Pump Performance'. Its presence alongside U1008 is extremely strong confirmation that the issue is within that specific circuit, as both codes are listed together in official TSBs. [2, 9, 16, 20, Bulletin #1804623, Bulletin #18-027-20]

Technical Service Bulletins (TSBs) & Recalls

• 1804623: Mentions U1008-00 - LIN 1 BUS as part of a list of potential DTCs that may illuminate the MIL.
• 21-032-20: Lists U1008-00 - LIN 1 Bus as a potential DTC.
• 18-027-20: Also lists U1008-00 - LIN 1 BUS among other potential codes.
• 18-045-23: Involves a PCM software update to address U1008 and improve the control strategy for the turbo coolant pump to protect turbo O-rings.

Platform-Specific Known Issues

• Several Technical Service Bulletins (TSBs), including #1804623, #21-032-20, and #18-027-20, list U1008 as a known fault code that can be set along with others, particularly P026E. [Bulletin #1804623, Bulletin #21-032-20, Bulletin #18-027-20]
• TSB #18-045-23 for the 2019 model year specifically involves a PCM software update that improves the 'Turbo coolant pump after run duration and on-off strategy update, to improve turbo O-ring durability', which is directly related to the system that triggers U1008.

Mechanic-Grade Diagnostic Values

• LIN Bus Voltage (at rest) — expected: Steady voltage approximately 1V less than battery system voltage (e.g., ~12V).. Failure: Voltage that is stuck low (near 0V) or missing entirely.
• LIN Bus Voltage (communicating) — expected: Toggling between ~1V (min) and ~12V (max). This requires a multimeter with a fast 'peak min/max' capture setting to see accurately.. Failure: A static voltage, or a voltage that does not toggle across the full range, indicates a communication breakdown, short, or open circuit.

Hidden / Shadow Codes Worth Checking

• U1008-08: LIN Bus - Bus Signal or Message Failure. The '-08' suffix is a failure type that specifies a general bus signal failure that cannot be assigned to a more specific sub-type. (see via This sub-code may only be visible on dealer-level diagnostic tools like wiTECH or advanced aftermarket scanners (e.g., MultiECUScan), while basic OBD-II readers may only show 'U1008'.)

Scan Tool Commands That Help

• wiTECH 2: BCM 'Proxi Alignment' — This procedure is required after reprogramming the PCM or replacing certain modules to ensure all vehicle modules correctly recognize each other on the network. A failed proxy alignment can cause communication errors.
• wiTECH 2: Reprogram PCM — Used to apply software updates released by Alfa Romeo via TSBs (like 18-045-23) that specifically address DTC U1008 and improve the control strategy of the auxiliary water pump.

Wiring & Ground Locations

• Remote Negative (-) Post — An exposed stud positioned next to the passenger side hood lock on the upper frame rail (on US models).. This is a primary grounding point for components in the engine bay. A loose or corroded connection here can cause intermittent and difficult-to-diagnose electrical issues, including LIN bus communication faults.

Real Owner Repair Stories

• Reddit user on r/AlfaRomeo (2019 Alfa Romeo Stelvio 2.2 Diesel (same platform and LIN bus architecture)) — Check engine light with codes P1104, P24A7, U05AA, and U0623 (Lost Communication With Radiator Shutter - another LIN device).
  ❌ Tried (didn't work) Replaced the auxiliary water pump with a new OEM part., Checked the fuse and relay for the pump circuit; both were good.
  ✅ What actually fixed it The user's problem was unresolved in the post, but their experience is highly valuable. After replacing the common parts (pump, relay), the codes remained. They were questioning if a bad ground or a required 'proxy alignment' after part replacement was the root cause, highlighting a critical next diagnostic step when the common fixes fail.

When the Usual Fixes Don't Work

• While the auxiliary pump relay is the most common cause for U1008, it is not the only cause. There are documented cases where owners have replaced the relay and even the pump itself, but the code persists. In these instances, the root cause was suspected to be more complex, involving either a wiring issue (such as a bad ground), or a module configuration problem requiring a 'Proxy Alignment' with a dealer-level scan tool after the new part was installed. This highlights that if the simple relay swap doesn't work, a deeper electrical and software-level diagnosis is necessary.

OEM Part Supersession History

• 06106094AA → 6106093AA — Likely an updated design to improve reliability, given the high failure rate of the original part.

Model Year Variations Within This Range

• 2017-2018: Earlier models within this range are more likely to have outdated PCM software. TSBs addressing U1008 are particularly relevant for these years, and checking for available software updates should be a higher priority during diagnosis compared to a 2019 model.