What Does P1235 Mean?
DTC P1235 indicates the fuel pump is not operating correctly at low speed. The fuel pump driver module has detected that the pump is not responding properly to low-speed commands, which are used during idle and light-load conditions to reduce noise and improve fuel economy. The pump may be running at full speed continuously or not running at all during low-speed commands.
Common Causes
30%
Fuel pump motor wearing out, unable to operate at lower voltages
25%
Fuel pump driver module low-speed output circuit failure
20%
High resistance in fuel pump wiring causing inadequate voltage at low-speed settings
15%
Fuel pump relay bypassing the FPDM and supplying full voltage constantly
10%
Contaminated fuel causing excessive pump load at low speed
Diagnostic Steps
1
Use a scan tool to command the fuel pump to low speed and monitor the actual pump current draw and duty cycle from the FPDM.
2
Measure voltage at the fuel pump connector while the FPDM commands low speed — voltage should be significantly below battery voltage (typically 6-9V).
3
Listen to the fuel pump operation — a pump that only runs at full speed (loud, constant whine) when low speed is commanded confirms the low-speed circuit issue.
4
Check fuel pressure at idle; if pressure is higher than specification, the pump may be running at full speed instead of low speed.
5
Inspect the fuel pump relay wiring to ensure it is routed through the FPDM and not bypassed.
Estimated Repair Cost
$150 - $700
Parts + labor, varies by vehicle and location
DTC P1235 indicates the fuel pump is not operating correctly at low speed. The fuel pump driver module has detected that the pump is not responding properly to low-speed commands, which are used during idle and light-load conditions to reduce noise and improve fuel economy. The pump may be running a...
The most common cause of P1235 (Fuel Pump Low Speed Malfunction) is: Fuel pump motor wearing out, unable to operate at lower voltages
Typical repair costs for P1235 range from $150 to $700, depending on the vehicle, location, and whether you do it yourself or go to a shop.
A fuel pump stuck at full speed increases noise and fuel consumption but is not immediately dangerous. However, continuous full-speed operation accelerates pump wear and can lead to eventual pump failure, which would cause a stall condition.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P1235 to identify the root cause.
OBDHut Mobile App
Scan codes directly from your car with the OBDHut app.
Coming Soon
Quick Info
Category
Powertrain
System
Fuel Delivery
Difficulty
Type
Manufacturer
Recommended Tools
OBD2 Scanner
A quality scan tool helps you read codes, view live data, and clear faults.
