P261A - Coolant Pump 'B' Control Circuit/Open
System
Powertrain (Engine & Gearbox)
Technical Description
The control module has detected a fault in the Coolant Pump 'B' Control Circuit/Open (P261A). The module sees no circuit at all — broken wire, backed-out pin, or a failed sensor.
Multimeter Test Points & Nominal Values
| Test Point / Component | Measurement | Nominal Target Range | Test Condition |
|---|---|---|---|
| Coolant Pump 'B' Control Circuit/Open – Permanent B+ Supply | Voltage (V) | 12.4 - 12.7 V (ignition OFF) / 13.5 - 14.7 V (engine running) | At module supply pins |
| Coolant Pump 'B' Control Circuit/Open – Ignition-Switched Supply | Voltage (V) | 11.8 - 14.4 V | Ignition ON |
| Coolant Pump 'B' Control Circuit/Open – Ground Connections Voltage Drop | Voltage (V) | < 0.1 V per ground point | Under load to battery negative |
| Coolant Pump 'B' Control Circuit/Open – 5 V Reference Outputs | Voltage (V) | 4.95 - 5.05 V per circuit | Ignition ON, sensors unplugged one at a time |
At module supply pins
Ignition ON
Under load to battery negative
Ignition ON, sensors unplugged one at a time
Oscilloscope Waveform Analysis
500 ms/div, 5 V/divPossible Causes
Open circuit, damaged wiring harness, or disconnected plug at Coolant Pump 'B' Control Circuit/Open
Channel B:Verify dedicated wiring pins and signal pair for circuit B against the schematic.
Chafed or pinched wiring harness along the signal path to Coolant Pump 'B' Control Circuit/Open
Poor ground connection or excessive voltage drop (> 0.1 V) at the ground point for Coolant Pump 'B' Control Circuit/Open
Defective internal output driver or reference circuit in the control module for Coolant Pump 'B' Control Circuit/Open
Symptoms
Recommended Solution
Compare signal voltage and resistance between circuit B and companion circuit A at module connector.
Verify continuity (< 0.5 Ω) on the signal wire between the component plug and the ECM header connector.
Verify loaded supply voltage and harness terminal pins at Coolant Pump 'B' Control Circuit/Open.
Check circuit continuity and ground-side voltage drop (< 0.05 V) for Coolant Pump 'B' Control Circuit/Open.
Inspect module enclosure and connector headers for water ingress, fretting corrosion, or PCB thermal damage.
Mechanic's Tip
When facing a 5V reference supply DTC, never replace the module first. A shorted external sensor (such as A/C pressure or EGR position) drags down the shared 5V internal rail. Unplug sensors one by one until 5V recovers.
Common Combinations
P261A, P261B, P261C VW 2.0 TDI EA288 – Elektrisk Kylvätskepump V488 Technical Diagnostic Guide
VOLKSWAGEN • 138 analyser
P261A, P00B7, P0234 Skoda Octavia 1.4 TSI – Laddluftkylare Vattenpump V188 Technical Diagnostic Guide
SKODA • 74 analyser