B1620 — Wiper Rear Low Limit Input Circuit Open

**Overview of the code**

The B1620 code indicates an issue related to the rear wiper system of a vehicle, specifically an open circuit in the low limit input. This means that the vehicle’s Electronic Control Unit (ECU) — the vehicle’s main computer — has detected a problem with the wiring or signal of the rear wiper’s low limit switch. It’s important to note that labeling and terminology can vary between different vehicle manufacturers, but the underlying issue remains similar across brands.

**Fast Facts**

System affected: Rear wiper control circuit
Severity: Moderate — can affect wiper operation but usually does not impair vehicle safety
Main symptoms: Wiper not stopping at the correct position, or the rear wiper behaving erratically
Driveability: No — this issue mainly affects the wiper operation, not vehicle driveability

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**Manufacturer variations for trouble code B1620**

Different vehicle manufacturers might assign different labels to similar issues. For the B1620 trouble code, the coding and labelling can differ depending on the OEM. Here are some known variations:

Volkswagen / Audi: « Rear Wiper Low Limit Input Circuit Open »
Ford: « Wiper Rear Low Limit Circuit Open »
BMW: « Rear Wiper Switch Low Limit Circuit Fault »
Renault: « Rear Wiper Low Limit Signal Error »
Mercedes-Benz: « Rear Wiper Low Position Circuit Open »

*Always refer to the specific OEM’s diagnostic trouble code (DTC) list, as labels may vary.*

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**What does trouble code B1620 mean?**

The B1620 code signals that the vehicle’s Electronic Control Module (ECU) has detected an abnormality in the rear wiper low limit input circuit. Essentially, the ECU expects a certain electrical signal from the wiper’s low limit switch — a device that detects when the wiper reaches its lowest position — and this signal is either absent or inconsistent.

The ECU monitors the input circuit— the wiring and connectors leading to the low limit switch — to ensure the wiper stops at the correct position. When the circuit is open (disconnected, broken, or faulty wiring), the ECU recognizes that the signal isn’t present as it should be, and triggers the B1620 code to alert the driver or technician of this issue.

This code typically appears in contexts where the wiper isn’t stopping or starting smoothly, or if there’s a fault detected during routine diagnostics or after a failed manual control attempt.

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**Severity & risks of trouble code B1620**

The B1620 code generally presents as a moderate issue. The main risk involves improper operation of the rear wiper — it might not stop at the correct position or may behave unpredictably. However, it does not typically affect the vehicle’s safety or driveability directly.

It’s unlikely to cause vehicle downtime or prevent driving altogether, but an unresolved rear wiper issue can diminish rear visibility, especially in adverse weather conditions, increasing the risk of poor rearward vision.

**Can the vehicle be driven?**

Yes. This fault primarily impacts the rear wiper function and does not hinder the fundamental operations required for driving safety.

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**Symptoms of trouble code B1620**

The presence of B1620 can manifest through various operational anomalies:

The rear wiper does not stop at the correct lower limit, perhaps continuing to wipe past the intended position.
The rear wiper is unresponsive or fails to operate on command.
Erratic or inconsistent wiper movement, possibly stopping and starting irregularly.
Warning message or warning light related to rear wiper on the dashboard.
Diagnostic trouble codes stored in the vehicle’s ECU without necessarily triggering an obvious symptom.

Many drivers notice their rear wiper functioning abnormally without other associated vehicle issues, which should prompt a diagnostic check.

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**Most likely causes of trouble code B1620**

Trouble codes like B1620 are usually linked to various wiring and sensor issues. Understanding these causes can help focus repairs effectively.

The most probable causes, ranked from most to least common, include:

Faulty or damaged wiring or connectors: Corrosion, broken wires, or poor connection in the circuit to the low limit switch can cause an open circuit.
Defective rear wiper low limit switch: The switch itself may be faulty or worn out, failing to send proper signals to the ECU.
Broken or disconnected wiring harness components: Damage during repairs, installation, or wiring degradation with age can lead to circuit issues.
Corrosion or dirt in connectors: Contaminants can interfere with electrical contact, mimicking an open circuit.
Malfunctioning ECU or software glitch: Although less common, a fault in the vehicle’s control unit can sometimes cause false readings.

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**How to diagnose trouble code B1620**

Diagnosing this issue should be approached systematically and safely.

Begin with a visual inspection for obvious damage or disconnections:

Check the wiring and connectors leading to the rear wiper low limit switch for signs of corrosion, damage, or disconnection.
Inspect the switch itself for physical damage or wear.
Use a multimeter to test continuity and voltage at the circuit connector, verifying proper wiring and signal flow.
Perform live data monitoring via the vehicle’s diagnostic scanner to see if the ECU receives the correct signals when the wiper moves.
Test the circuit for any intermittent faults or shorts.
Clear the codes and operate the rear wiper to see if the fault reoccurs, observing the switch and circuit operation during testing.

It is recommended that complex diagnosis or repairs involving wiring and the control unit be performed by a certified technician.

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**Possible repairs for trouble code B1620**

Once a diagnosis confirms the cause, repairs should be tailored to the identified issue.

Repairs may include:

Replacing damaged wiring or connectors: Basic repair that can often be performed by a competent DIYer or technician.
Replacing the rear wiper low limit switch: Usually a straightforward replacement, but some vehicles may require partial disassembly.
Repairing or re-securing wiring harnesses: Ensuring all connectors are clean, properly seated, and free of corrosion.
Cleaning or replacing affected connectors: To restore proper electrical contact.
Reprogramming or updating the ECU software: Only if a software glitch is suspected, performed by professional diagnostics.

In cases where the fault is not clear or the problem persists after repairs, professional diagnosis is advised.

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**Vehicles commonly associated with trouble code B1620 in Europe**

This code does not appear exclusively in certain brands but is more frequent in specific vehicle models with rear wiper systems. In Europe, vehicles from brands such as:

Volkswagen Group (VW, Audi): Especially models with electronically controlled rear wipers.
Ford: Certain models with rear wipers integrated into their electrical system.
BMW: Rear wiper systems in various models using electronic limit switches.
Renault and Peugeot: Models with electronically controlled rear washer and wiper assemblies.

are often associated with this code during diagnostic processes. It’s important to refer to manufacturer-specific technical documentation for precise vehicle applicability.

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**Frequent mistakes with trouble code B1620**

Diagnosing and repairing B1620 can sometimes lead to common errors, which should be avoided:

Ignoring visual inspection: Jumping straight into electrical tests without checking wiring and connectors.
Replacing parts without proper diagnosis: Swapping the switch or wiring harness prematurely, leading to unnecessary repairs.
Using incompatible repair parts: Installing non-OEM replacements that may not match specifications.
Overlooking contamination or poor contact issues: Failing to clean or inspect connectors thoroughly.
Failing to clear codes properly after repairs: Not resetting the ECU, which may hide persistent faults or show false positives in diagnostics.

Following a systematic approach and adhering to best practices minimizes misdiagnosis and ensures effective repair.

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**FAQ — trouble code B1620**

**Can this code disappear on its own?**

No. The B1620 code results from a hardware or wiring fault that won’t resolve spontaneously. It requires inspection and repair.

**Can I keep driving?**

Generally, yes. Since the issue affects only the rear wiper operation, it does not impair the core functions of the vehicle. However, poor rear visibility in bad weather conditions should be considered.

**Why does the code return after clearing it?**

Because the underlying fault has not been fixed. If wiring, switch, or connection issues persist, the ECU will detect the problem again and re-trigger the code.

**Is this a urgent repair?**

Not immediately. While it’s good practice to fix electrical issues to ensure proper vehicle operation and avoid further damage, this fault is not safety-critical.

**Summary**

The B1620 trouble code is a diagnostic indicator of an open or faulty circuit in the rear wiper’s low limit position input. While not crucial to vehicle safety or driveability, it impacts rear wiper performance and should be addressed appropriately through inspection and targeted repairs. Proper understanding of the specific wiring, switch function, and connector integrity is essential for a reliable fix and ensuring the vehicle’s rear window remains free of obstructions for safe driving conditions.