After a startup when engine is cold there is no brake assist, the brake pedal feels very hard, braking efficiency is very low and for some reason it feels worse when driving in reverse.
2006 V70 brake Vacuum pump/switch 31317445 31265825
dan777 »
I finally decided to fix an annoying problem that I was having for a while when basically there is no brake assist when engine is cold.
I know there were some other posts dealing with this issue but I thought that would be very helpful to write a detailed tutorial with pictures about how to diagnose and eventually fix the problem. This should point people in the right direction and prevent them wasting time checking the whole brake system when the issue is somewhere else.
Symptoms
After a startup when engine is cold there is no brake assist, the brake pedal feels very hard, braking efficiency is very low and for some reason it feels worse when driving in reverse.
Normal operation
The brake assist needs vacuum and after the engine was stopped for a while there is not enough vacuum left in the system. After a minute or so the engine produces enough vacuum for the brake booster. To compensate this there is an electrical vacuum pump that it activated by a vacuum switch when the vacuum is too low. When the vacuum is back to normal the switch disconnects the pump, which is not designed to run for an extended period of time.
Issues: If the switch contacts get sticky then the pump runs for too long and eventually it will fail or burn the fuse. If the switch contacts are not closing properly then the pump will not start.
Tools
Tools needed for diagnose and pump replacement:
T25 torx screwdriver, 10 wrench and rachet, voltmeter, pliers
Diagnose
1.Locate the vacuum switch between the air box and the front driver side lamp.
2.Turn the key in position II. Disconnect the orange connector and measure the voltage between the ground and the contact as shown. If the fuse is OK then it should be 12V DC on one of the contacts, if not then replace fuse 33 (20A) located behind the plastic cover below the steering wheel.
3.Disconnect the hose on the right side of the switch (some hissing is normal) and measure the impedance between the switch contacts.
Because there is no vacuum the contacts should be closed so impedance should be zero. If the contacts are open (infinite impedance) then the switch is bad and needs to be replaced. Reconnect the hose and start the engine. The brake pedal will be very hard at the beginning. After it feels normal again (vacuum is OK now) then measure the impedance again, the contacts should be open now. If they are still closed the switch is bad and probably the vacuum pump is burned too. Stop the engine and remove the key.
Switch replacement is very easy, just disconnect all 3 hoses and the electrical connector, be careful to put it back the same way with the orange connector towards the lamp, otherwise you will not have brake assist at all!!!
Vacuum pump replacement
1.Remove the air box cover.
2.Remove the MAF connector. Be carefull when pulling the connector clamp, do not use a screwdriver.
3.Remove the air intake duct as shown (2 torx screws). There is a circular ruber seal that might get out, just push it back in. Other method is to remove the clamp and pull out the duct but is not that easy, you might need to use a heat gun…)
4.Remove all the parts attached to the air box (air duct, turbo valve, hose, wires as shown)
5.Pull the air box out (this is somewhat a scary procedure but it works every time, there are 3 plastic holders at the bottom you just have to pull hard).
6.Remove the plastic seat under the air box (3 screws).
7.Remove he hose connected to the vacuum pump.
8.Remove the metallic bracket that holds the vacuum pump as shown (2 screws).
9.Replace the vacuum pump (2 screws). The new one came with new rubber bushings but the old screws did not fit through them so I reused the old ones.
10.Transfer the snap-on coupling (press on the green tab and pull the coupling out)
11.Put everything back in reverse order. At the end everything should look like this:
I bought the parts from FCP:
$179.55 for the Pump – 31317445
$8.99 for the Snap-on Coupling – 30744403
$59.95 for the Vacuum Switch – 31265825
No Brakes When Cold – Vacuum Pump/Switch Replacement with Pics
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1 Comment
Very well done; clear, well explained, labelled (circles) with good pics.